# QM 2011 - XXII International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

Europe/Zurich
Théâtre National (Centre Bonlieu)

### Théâtre National

#### Centre Bonlieu

France
,
Description

Quark Matter Conference in 2011 at Annecy ( back to QM2011 home page )

Support
• Sunday, May 22
• 8:30 AM
STUDENTS only: Collection of entrance badges must be collected from 8:30 to 12:00 Imperial Palace, Annecy

#### Imperial Palace, Annecy

• Student lectures Salle de l'Europe (Imperial Palace)

### Salle de l'Europe

#### Imperial Palace

• 1
Heavy-ion collisions and QCD: the big picture Salle de l'Europe (Imperial Palace, Annecy)

### Salle de l'Europe

#### Imperial Palace, Annecy

Speaker: Francois Gelis (IPhT Saclay)
• 2
Soft physics and hydrodynamics Salle de l'Europe (Imperial Palace, Annecy)

### Salle de l'Europe

#### Imperial Palace, Annecy

Speaker: Paul Romatschke (Frankfurt Institute for Advanced Studies)
• 10:30 AM
Coffee break Salon le Foyer (Imperial Palace)

### Salon le Foyer

#### Imperial Palace

• 3
Jets, high-pT hadrons and prompt photons Salle de l'Europe

### Salle de l'Europe

#### Imperial Palace

Speaker: Marco van Leeuwen (Utrecht University)
• 4
Heavy-quarks and quarkonia Salle de l'Europe

### Salle de l'Europe

#### Imperial Palace

Speaker: Roberta Arnaldi (Universita degli Studi di Torino)
• 12:20 PM
Lunch Break Salon Brasserie du Parc / Le Rendez-Vous (Imperial Palace, Annecy)

### Salon Brasserie du Parc / Le Rendez-Vous

#### Imperial Palace, Annecy

• Famous plot session Salle de l'Europe (Imperial Palace)

### Salle de l'Europe

#### Imperial Palace

• 5
Initial conditions, low-x QCD, thermalization
Speaker: David d'Enterria (CERN)
• 6
Speaker: Dr Panos Christakoglou (NIKHEF - Utrecht University)
• 7
Jets, high-pT hadrons, and prompt photons
Speaker: Konrad TYWONIUK (University of Lund)
• 8
Heavy-quarks and quarkonia
Speaker: Agnes Mocsy (Pratt Institute, NY, USA)
• Parallel discussion 1: Initial conditions, low-x QCD, thermalization Salle Ravel A (Imperial Palace)

### Salle Ravel A

#### Imperial Palace

Conveners: David d'Enterria, François Gelis
• Parallel discussion 2: QCD phase transition, hydrodynamics, hadronization Salle de l'Europe (Imperial Palace)

### Salle de l'Europe

#### Imperial Palace

Conveners: Dr Panos Christakoglou (NIKHEF - Utrecht University), Paul Romatschke (FIAS Frankfurt)
• Parallel discussion 3: Jets, high-pT hadrons, prompt photons Salon Ravel B (Imperial Palace)

### Salon Ravel B

#### Imperial Palace

Conveners: Dr Konrad Tywoniuk (Universidade de Santiago de Compostela), Marco van Leeuwen (Utrecht University)
• Parallel discussion 4: Heavy-quarks and quarkonia Salon Haendel AB (Imperial Palace)

### Salon Haendel AB

#### Imperial Palace

Convener: Roberta Arnaldi (Universita degli Studi di Torino)
• 4:00 PM
Coffee break Foyer (Imperial Palace)

### Foyer

#### Imperial Palace

• Parallel discussion 1: Initial conditions, low-x QCD, thermalization Salle Ravel A (Imperial Palace)

### Salle Ravel A

#### Imperial Palace

Conveners: David d'Enterria (CERN), Francois Gelis
• Parallel discussion 2: QCD phase transition, hydrodynamics, hadronization Salle de L'Europe (Imperial Palace)

### Salle de L'Europe

#### Imperial Palace

Conveners: Dr Panos Christakoglou (NIKHEF - Utrecht University), Paul Romatschke (FIAS Frankfurt)
• Parallel discussion 3: Jets, high-pT hadrons, prompt photons Salon Ravel B (Imperial Palace)

### Salon Ravel B

#### Imperial Palace

Conveners: Dr Konrad Tywoniuk (Universidade de Santiago de Compostela), Marco van Leeuwen (Utrecht University)
• Parallel discussion 4: Heavy-quarks and quarkonia Salon Haendel AB (Imperial Palace)

### Salon Haendel AB

#### Imperial Palace

Convener: Roberta Arnaldi (Universita degli Studi di Torino)
• Collection of entrance badges for all registrants - badges are obligatory in order to enter the QM site Théâtre National

### Théâtre National

#### Centre Bonlieu

France
• Monday, May 23
• 7:30 AM
Collection of entrance badges for all registrants - badges are obligatory in order to enter the QM site from 8:30 to 12:00 Théâtre National

### Théâtre National

#### Centre Bonlieu

France
• Overviews: LHC & Theory Théâtre National

### Théâtre National

#### Centre Bonlieu

1 Rue Jean Jaurès, 74000 Annecy, France Tel : +33 4 50 45 00 33
Convener: Urs Wiedemann (CERN)
• 9
LHC accelerator
Speaker: Steve Myers (CERN)
• 10
Theory overview
Speaker: Prof. Krishna Rajagopal (MIT)
• 11
Opening Théâtre National

### Théâtre National

#### Centre Bonlieu

France
• 10:10 AM
Coffee break Théâtre National

### Théâtre National

#### Centre Bonlieu

France
• Overviews: Experiments Théâtre National

### Théâtre National

#### Centre Bonlieu

1 Rue Jean Jaurès, 74000 Annecy, France Tel : +33 4 50 45 00 33
Convener: Christelle Roy (Institut Pluridisciplinaire Hubert Curien (IPHC))
• 12
PHENIX Highlights
After establishing the creation of dense partonic matter in the early years of RHIC, the focus of recent experimental and theoretical effort has been to determine the properties of this partonic medium. With the advent of the LHC, there is now a new aspect to this quest: are the properties of the medium created at the LHC different from that created at RHIC? In this light, we will present the latest experimental results of the PHENIX collaboration, further constraining the properties of the sQGP at RHIC.
Speaker: Dr Stefan Bathe (RIKEN-BNL Research Center)
• 13
STAR highlights
Speaker: Hiroshi Masui (LBNL)
• 14
Overview of the experimental results by the ALICE Collaboration
In this talk we summarize the results obtained by ALICE Collaboration in the first Pb-Pb run at LHC.
Speaker: Juergen Schukraft (CERN)
• 15
Speaker: Peter Steinberg (Brookhaven National Laboratory)
• 16
Overview of the experimental results by the CMS Collaboration
We will present early results of the CMS experiment from PbPb collisions at √sNN = 2.76 TeV, probing quark and gluon matter at unprecedented values of energy density. The capabilities of the CMS apparatus allows us to investigate various hard probes, as well as bulk particle production and collective phenomena, using the calorimetry, muon and tracking systems covering a large range in pseudorapidity, complemented by a flexible two-level trigger system.
Speaker: Bolek Wyslouch (MIT)
• 12:45 PM
Lunch break Restaurant La Voile, Brasserie du Parc/Rotonde du Parc (Impérial Palace)

### Restaurant La Voile, Brasserie du Parc/Rotonde du Parc

#### Impérial Palace

rest.la voile 200p - brasserie du Parc/Rotonde du parc 500p

• Correlations and fluctuations Rotonde de l'Europe (Imperial Palace)

### Rotonde de l'Europe

#### Imperial Palace

Convener: Jens-Jorgen Gaardhoje (Niels Bohr Institute)
• 17
Observation of a ridge correlation structure in high multiplicity pp collisions with CMS
Results on two-particle angular correlations are presented in proton-proton collisions at center of mass energies of 0.9, 2.36, 2.76 and 7 TeV, over a broad range of pseudorapidity and azimuthal angle. In very high multiplicity events at 7 TeV, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate $p_T$ of 1-3 GeV/c, in the kinematic region 2.0 $< |\Delta\eta| <$ 4.8 and small \Delta\Phi. This structure, which has not been observed in pp collisions before, is similar to what is known as the "ridge" in heavy ion collisions. It is not predicted by commonly used proton-proton Monte Carlo models and is not seen in lower multiplicity pp collisions. Updated studies of this new effect as a function of particle transverse momentum, rapidity and event characteristics are shown and discussed in comparison to various model calculations.
Speaker: Dragos Velicanu (MIT)
• 18
Anisotropic flow of charged particles at 2.76 TeV measured with the ALICE detector
Ante Bilandzic for the ALICE collaboration Measurements of anisotropic flow provided evidence for the creation of strongly interacting matter which appears to behave as an almost ideal fluid. Anisotropic flow signals the presence of multiple interactions and is very sensitive to the initial spatial anisotropy of the overlap region in non-central heavy-ion collisions. In this talk we report measurements of elliptic v2, triangular v3, quadrangular v4 and pentagonal v5 flow. These measurements have been performed with two- and multi-particle correlation techniques. We will show how these measurements can be understood from the initial spatial anisotropy and its fluctuations. These observations provide a possible explanation for the away-side features often attributed to Mach cone effects.
Speaker: Ante Bilandzic (NIKHEF)
• 19
Eccentricity and elliptic flow in proton-proton collisions from parton evolution
It has been argued that high-multiplicity proton-proton collisions at the LHC may exhibit collective phenomena usually studied in the context of heavy-ion collisions, such as elliptic flow. We study this issue using DIPSY, a brand-new Monte Carlo event generator which features almost-NLL BFKL dynamics and describes the transverse shape of the proton including all fluctuations. We predict the eccentricity of the collision as a function of the multiplicity and estimate the magnitude of the elliptic flow. We then compare the result with correlation from "nonflow" effects and suggest how to suppress the latter by applying cuts in the final state.
Speaker: Dr Yoshitaka Hatta (University of Tsukuba)
• 20
Dynamical $K/\pi$, $p/\pi$, and $K/p$ fluctuations in $\sqrt{s_{NN}}$ = 7.7-200 GeV Au+Au collisions
Terence J Tarnowsky (for the STAR Collaboration) Dynamical fluctuations in global conserved quantities such as baryon number, strangeness, or charge may be observed near a QCD critical point. Results from new measurements of dynamical $K/\pi$, $p/\pi$, and $K/p$ ratio fluctuations are presented. The commencing of a QCD critical point search at RHIC has extended the reach of possible measurements of dynamical $K/\pi$, $p/\pi$, and $K/p$ ratio fluctuations from Au+Au collisions to lower energies. The STAR experiment has performed a comprehensive study of the energy dependence of these dynamical fluctuations in Au+Au collisions at the energies $\sqrt{s_{NN}}$ = 7.7, 11.5, 39, 62.4, and 200 GeV. New results are compared to previous measurements and to theoretical predictions from several models. The measured dynamical $K/pi$ fluctuations are found to be independent of collision energy, while dynamical $p/\pi$ and $K/p$ fluctuations have a negative value that increases toward zero at top RHIC energy.
Speaker: Terence Tarnowsky (Michigan State University)
• 21
Determining initial state fluctuations from flow measurements
Long-range azimuthal correlations are generated by fluctuations of the initial energy distribution, followed by collective flow. We list eight independent observables which can be measured using multiparticle azimuthal correlations in the first three Fourier harmonics. Some of these observables are already well known, such as $v_2\{2\}$ and $v_2\{4\}$, but most of them are new, in particular, the joint correlations between $v_1$, $v_2$ and $v_3$. We show that by taking ratios of these observables, one can construct quantities which are largely independent of the hydrodynamic response of the medium, and thus are solely determined by initial fluctuations. We present predictions for these ratios using a Monte-Carlo Glauber model and a Monte-Carlo KLN model, and compare to existing data from STAR and ALICE.
Speaker: Dr Jean-Yves Ollitrault (SPhT, Saclay)
• 22
Initial condition fluctuations in heavy ion collisions
We investigate the effect of event-by-event fluctuations and the degree of granularity in the initial conditions on the collective evolution of matter created in heavy-ion collisions using fluid dynamics. Motivated by the glasma-flux-tube scenario, we model the initial condition by a set of randomly distributed longitudinal tubes in a boost-invariant 2D geometry. The model introduces two parameters: the number of tubes in each event and the transverse (gaussian) width in energy density of a tube. The number of tubes fluctuates event by event and the width of the tubes introduces a granularity to the initial condition. Both parameters strongly affect the hydrodynamical evolution. For instance, we observe that the increasing granularity reduces the slope of the transverse momentum spectra, decreases the value of the differential elliptic flow at the average transverse momentum, and generates a double-peak structure in the two-particle distribution. With this framework, we aim to constrain the initial condition of a heavy-ion collision by performing a systematic analysis of the effects of each parameter on the final observables.
Speaker: Philippe Mota (Institut für Theoretische Physik, Goethe-Universität)
• Global and collective dynamics Salle de l'Europe (Imperial Palace)

### Salle de l'Europe

#### Imperial Palace

Convener: Barbara Erazmus (CNRS/IN2P3)
• 23
The second act of hydro: shocks and sounds from initial perturbations and jets
Recently there was significant progress in account for several lower harmonics of the Little Bang", especially the so called triangular flow, ascribed to fluctuations of the initial conditions. We discuss this problem more generally, combining many harmonics coherently into certain patterns of sound propagation. Analytic solution for all harmonics is found for the so called Gubser flow", with complete Green function obtained. Another source of perturbations which can be studied using our results are waves induced by quenching jets. We argue that for large energy loss shock waves should form, as well as the so called jet/fireball edge, separating unperturbed and excited matter. We discuss how this edge should be visible experimentally, perhaps on \ event-by-event basis.
Speaker: Edward Shuryak (Stony Brook University)
• 24
Charged-particle multiplicity, centrality and the Glauber model with ALICE at 2.76 ATeV
The measurements of charged-particle multiplicity and transverse energy in Pb-Pb collisions at 2.76 ATeV are reported as a function of centrality. The fraction of inelastic cross section seen by the ALICE detector is estimated using a Glauber model or correcting the data by simulations. The results scaled by the number of participating nucleons are compared with pp collisions at the same collision energy and to similar results obtained at the significantly lower energies, and with models based on different mechanisms for particle production in nuclear collisions. Particular emphasis will be given to a discussion on systematic studies of the dependence of the centrality determination on the Glauber model, and the validity of the Glauber model at 2.76 TeV.
Speaker: Constantinos Loizides (Lawrence Berkeley National Lab. (LBNL))
• 25
Pseudorapidity dependence of charged hadron multiplicity and transverse energy densities in PbPb collisions from CMS
The pseudorapidity and centrality dependence of transverse energy and charged particle multiplicities offers insight into the properties of the matter produced in the collisions of ultra-relativistic heavy nuclei. Multiplicities as a function of center-of-mass energy and collision centrality are important for exploring the role of hard and soft scattering in particle production and for looking at novel effects in nucleus-nucleus collisions (e.g. scaling, saturation). Measurements of the charged hadron multiplicity and transverse energy are presented for minimum bias PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair. The number of charged hadrons was obtained by two different methods based on the inner silicon pixel system of the CMS detector at the LHC. One technique involved counting the number of reconstructed single particle hits in the pixel detector, while the other formed hit pairs ('tracklets') from the different detector layers. The two methods are in excellent agreement. For the transverse energy measurement, CMS has almost hermetic calorimetry coverage with fine granularity and excellent resolution. In addition for particles near central rapidity momenta from the tracker can be combined with the calorimeter data to give a significant improvement of the system resolution. The measurements is compared with heavy-ion results from earlier experiments, where a smooth dependence on the collision energy is observed. The results as a function of centrality are compared to the corresponding value in pp collisions interpolated from existing CMS measurements
Speaker: Krisztian Krajczar (KFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences)
• 26
Measurement of charged particle pseudorapidity density in PbPb collisions at sqrt(s_NN) = 2.76 TeV with the ATLAS detector at the LHC
Charged particle multiplicity is an important bulk observable for heavy ion collisions. It measures the global features of the medium produced and constrains the initial conditions of the system. It also provides an important test for dynamical model calculations which predict the dependence of multiplicity on centrality at RHIC and the LHC. We present the study of charged particle pseudorapidity density distributions over a broad range of pseudorapidity and centrality in Pb+Pb collisions at √sNN = 2.76 TeV with the ATLAS detector at LHC. The centrality dependence of the particle density near mid-rapidity scaled by the number of participating nucleon pairs (dNch/dη(|η| < 0.5)/(0.5Npart)) is presented. Comparisons with results from previous measurements are used to study the collision energy dependence. The pseudorapidity distributions measured over four units of pseudorapidity are compared with those of different collision systems and energies as well as dynamical models.
Speaker: Yujiao Chen (Columbia University)
• 27
Spectra, flow and HBT in PbPb collisons at the LHC
The expansion of the fireball created in Pb-Pb collisions at $\sqrt{s}=2.76$TeV is modelled using the relativistic viscous hydrodynamics. The experimentally observed interferometry radii are well reproduced. The recent data of the ALICE Collaboration on the elliptic flow as function of the centrality can be very well described using the hydrodynamic expansion of a fluid with a small shear viscosity $\eta/s=0.08$. The elliptic flow as function of the transverse momentum shows systematic deviations from a hydrodynamic behavior in the small momenta region $p_\perp<800$MeV. It indicates that a non-negligible contribution of non-thermalized particles from jet fragmentation is present.
Speaker: Piotr Bozek (IFJ PAN Krakow/ Rzeszow University)
• 28
Diffraction dissociation of protons in proton-proton collisions at \sqrt{s} = 0.9 TeV, 2.76 TeV and 7 TeV with ALICE at the LHC
(for the ALICE Collaboration) The relative rates of single‐ and double‐ diffractive processes were measured with the ALICE detector by studying properties of gaps in the pseudorapidity distribution of particles produced in proton‐proton collisions at \sqrt{s} = 0.9 TeV, 2.76 TeV and 7 TeV. ALICE triggering efficiencies were determined for various classes of events, using a detector simulation validated with data on inclusive particle production. Cross‐sections were determined using van der Meer scans to measure beam properties.
Speaker: Dr Martin Poghosyan (Universita & INFN, Torino)
• Hadron thermodynamics and chemistry Salon Haendel AB (Imperial Palace)

### Salon Haendel AB

#### Imperial Palace

Convener: Xin-Nian Wang (Unknown)
• 29
Observation of the antimatter helium-4 nucleus
We present the observation of the antimatter $^{4}He$ nucleus, the heaviest observed antinucleus. The identification and measurement of anti-$^{4}He$ relies on the mean energy loss per unit track length, the time of flight of particles, and their curvature in the magnetic field of the STAR detector. Another essential detector capability was the High Level online tracking Trigger (HLT), which helps to cope with the large data volume and greatly speeds up the search effort. In total, 18 anti-$^{4}He$ counts were detected at the STAR experiment at RHIC in $10^{9}$ recorded Au+Au collisions at beam energies of $\sqrt{s_{NN}}$ = 200 GeV and 62 GeV. Misidentification probability is estimated to be below $10^{-11}$. The invariant differential cross section is consistent with expectations from thermodynamic and coalescent nucleosynthesis models, which has implications for future production of even heavier antimatter nuclei, as well as for experimental searches for new phenomena in the cosmos. The yield of the stable antinucleus next in line (mass number = 6) is predicted to be down by a factor of $2.6 X 10^{6}$ compared to anti-$^{4}He$ and is beyond the reach of current accelerator technology.
Speaker: Liang Xue (SINAP/BNL)
• 30
Particle identification in the ALICE experiment
The particle identification capabilities of the ALICE experiment are unique among the four major LHC experiments. The working principles, the strategies for signal extraction, and excellent performance of the central barrel detectors in a high-multiplicity environment will be presented. The particle identification of the Inner Tracking System (ITS) and the Time Projection Chamber (TPC) are based on the specific energy loss whereas the Time-Of-Flight detector (TOF) determines the particle velocity by measuring its flight time. Thus low momenta charged kaons, pions, protons, deuterons, tritons, helium-nuclei, and their respective anti-particles can be identified from 100 MeV/c up to several GeV/c in momentum and the corresponding spectra and yields can be extracted. Weak decays of strange particles can be identified via their particular kink and V0 topologies and the precise determination of the first and secondary vertices. The pT-reach of hadron identification can be extended using Cherenkov-radiation in the High Momentum Particle Identification detector (HMPID) and by the relativistic rise in the ionization measurement of the TPC. Electron identification at higher momenta is achieved by the detection of transition radiation in the Transition Radiation Detector (TRD).
Speaker: Alexander Philipp Kalweit (Technische Universität Darmstadt)
• 31
Measurement of $\pi$/K/p spectra with ALICE in proton-proton collisions at $\sqrt{s} = 900$ GeV and $\sqrt{s} = 7$ TeV
The ALICE experiment features several particle identification systems, which allow us to measure spectra in a broad range of transverse momentum $p_{\mathrm{t}}$ from 100 MeV/c up to a few GeV/c. New results on identified charged particle $p_{\mathrm{t}}$ spectra measured in proton-proton collisions at $\sqrt{s}=7$ TeV will be presented. They will be compared to results obtained at 900 GeV and lower energies, theoretical models and commonly used event generators. The large statistics collected in collisions at $\sqrt{s} = 7$TeV allows us to measure the spectra and yields as a function of the event multiplicity, reaching a $dN/d\eta$ comparable to nuclear collisions at lower energy. The status and perspective of such measurement will also be presented.
Speaker: Marek Chojnacki (UU/NIKHEF)
• 32
Validity of the hadronic freeze-out curve
Speaker: Reinhard Stock (Institut fuer Kernphysik - Johann-Wolfgang-Goethe Univ.)
• 33
Production of neutral pions and eta-mesons in pp collisions measured with ALICE
The inclusive production of $\pi^0$ and $\eta$ mesons is measured at mid-rapidity in pp collisions over a wide transverse momentum ($p_T$) range with the ALICE experiment at $\sqrt{s}$=900GeV, 2.76~TeV and 7~TeV. The mesons are measured via two different techniques: with the calorimeters (PHOS and EMCAL) and via photon conversions reconstructed in the Central Tracking System. A systematic comparison to next-to-leading order pQCD (NLO) calculations for $\pi^0$ and $\eta$ mesons as well as the $\sqrt{s}$-dependence of the $\pi^0$ production is presented. Furthermore, the $\eta$ to $\pi^0$ ratio as well as the corresponding NLO calculations are discussed. The presented data serves as a baseline both for the decay photon background for direct photon measurements as well as for the background of electrons in open heavy flavor measurements. It will then be used to calculate the nuclear modification factor, R$_{AA}$, in heavy-ion collisions with ALICE.
Speaker: Dr Klaus Reygers (University of Heidelberg)
• 34
Resonance measurement in pp and PbPb collisions at LHC with the ALICE detector
The study of resonances production in pp collisions contributes to the proper tuning of the QCD-inspired particle production models and to the better understanding of the underlying event, while in PbPb collisions resonances are good probes to estimate the collective properties of the fireball, and in particular its lifetime. Strange resonances can also contribute to the historical topic of strangeness production measurement. pT spectra have been measured for φ, K ∗ , Σ∗ and Ξ∗ resonances using data from pp collisions at 7 TeV in LHC, measured by the ALICE detector. Mesons were analyzed in a rapidity window of ±0.5 while baryons in a window of ±0.8. Results will be shown from comparisons with several MC models, which show in general an acceptable match, except for the Ξ∗ which appear to be underestimated. Moreover, first results from the analysis of φ resonance in Pb-Pb collisions at 2.76 ATeV will be presented.
Speaker: Dr Alberto Pulvirenti (University / INFN Catania)
• Theory developments Salon Ravel AB (Imperial Palace)

### Salon Ravel AB

#### Imperial Palace

Convener: Kari J. Eskola (University of Jyvaskyla)
• 35
Chirality, magnetic field and parity violation in hot QCD matter
An overview of the recent progress in understanding the interplay of quantum anomalies, chirality, and magnetic field in the dynamics of QCD fluid will be presented. The current theoretical description of the chiral magnetic and chiral vortical effects within anomalous magnetohydrodynamics will be described. It allows a quantitative approach to these phenomena in heavy ion collisions, and the first results from such studies will be reviewed. The existing and future experimental measurements needed to establish or refute the local violation of parity in hot QCD matter will be discussed.
Speaker: Prof. Dmitri Kharzeev (Stony Brook and BNL)
• 36
Equilibration and Thermalization of Strongly Coupled Field Theories
Using the AdS/CFT correspondence, we probe the scale-dependence of thermalization in strongly coupled field theories following a quench, via calculations of 2-point functions, Wilson loops and entanglement entropy in 2, 3, and 4 dimensions. In the saddlepoint approximation these probes are computed in AdS space in terms of invariant geometric objects -- geodesics, minimal surfaces and minimal volumes. Our calculations for two dimensional field theories are analytical. In our strongly coupled setting, all probes in all dimensions share certain universal features in their thermalization: (1) a slight delay in the onset of thermalization, (2) an apparent non-analyticity at the endpoint of thermalization, (3) top-down thermalization where the UV thermalizes first. For homogeneous initial conditions the entanglement entropy thermalizes slowest, and sets a time scale for equilibration that saturates a causality bound over the range of scales studied. The growth rate of entanglement entropy density is nearly volume-independent for small volumes, but slows for larger volumes.
Speaker: Berndt Mueller (Duke University)
• 37
Interference effects in medium--induced gluon radiation
The recent results at the LHC on jet quenching in heavy ion collisions call for a fundamental understanding of the evolution of a relatively hard jet propagating through a QCD medium like the quark--gluon plasma. As a first step in that sense, we consider the interference pattern for the medium--induced gluon radiation produced by a color singlet quark--antiquark antenna embedded in a QCD medium with size $L$. This setup is indeed well suited for studies of coherence phenomena like angular ordering. We focus on the most favorable kinematics for medium--induced gluon radiation in the BDMPS--Z regime, that is transverse momenta $k_\perp \sim \sqrt{\hat q L}$, short formation times $\tau_f \ll L$, and relatively large emission angles $\theta \gtrsim \theta_f\equiv(\hat q/\omega)^{1/3}$ ($\hat q$ is the medium jet quenching' parameter and $\omega$ is the gluon energy). We demonstrate that, for a dipole opening angle $\theta_{q\bar q}$ larger than $\theta_f$, there is no interference between medium--induced gluon emissions by the quark and the antiquark. That is, the in--medium contribution to the antenna pattern is the incoherent superposition of two individual BDMPS--Z spectra. Physically, this is so since, unlike the direct emissions which can be delocalized anywhere throughout the medium, the interference terms are non--zero only for the very early emissions, such that the size of the $q\bar q$ dipole at the time of emission be smaller than the transverse wavelength of the emitted gluon.
Speaker: Dr Jorge Casalderrey Solana (CERN)
• 38
Jets in QCD media: from color coherence to decoherence
Jet physics in hadronic collisions is one of the major achievements of perturbative QCD. However, a complete theory of jets in a hot and dense partonic environment remains to be developed. Such a theory is needed in Heavy-Ion Collisions (HIC), at RHIC and now at the LHC, in order to have a clean access to the properties of the Quark-Gluon Plasma (QGP). To this end, we have investigated medium modification of the radiation pattern of a quark-antiquark antenna traversing a dense medium in order to understand how the QGP alters color coherence which is an important feature of the intRAjet structure in vacuum. In contrast to gluon radiation in vacuum, and unexpectedly, we find a strict geometrical separation between in-vacuum and medium-induced gluon radiation. Also, a soft logarithmic divergence appears pointing to the possibility of resuming multiple gluon branching in the cascade. Moreover, in the case of an opaque medium near the unitarity bound, a simple and intuitive physical picture arises : the interaction with the QGP leads to the gradual decoherence of the pair yielding a universal radiation pattern which does not depend on the initial color configuration of the antenna. These results are in qualitative agreement with the recent ATLAS and CMS data and provide a starting point for further studies on in-medium jet modification.
Speaker: Dr Yacine Mehtar-Tani (University of Santiago de Compostela)
• 39
Running coupling corrections to high energy inclusive gluon production
We calculate running coupling corrections for the lowest-order gluon production cross section in high energy hadronic and nuclear scattering using the BLM scale-setting prescription. In the final answer for the cross section the three powers of fixed coupling are replaced by seven factors of running coupling, five in the numerator and two in the denominator, forming a 'septumvirate' of running couplings, analogous to the 'triumvirate' of running couplings found earlier for the small-x BFKL/BK/JIMWLK evolution equations. We use our lowest-order result to conjecture how running coupling corrections may enter the full fixed-coupling kT-factorization formula for gluon production which includes non-linear small-x evolution. This work is the latest theoretical improvement on the approach used recently by Albacete and Dumitru in arXiv:1011.5161 [hep-ph] to accurately predict the centrality dependence of the charged particle multiplicity density measured by ALICE collaboration.
Speaker: Prof. Yuri Kovchegov (The Ohio State University)
• 40
Next-to-leading order structure function for DIS off a large nucleus
The high-energy behavior of amplitudes in gauge theories can be reformulated in terms of the evolution of Wilson-line operators. In the leading order this evolution is governed by the non-linear Balitsky-Kovchegov (BK) equation. In order to see if this equation is relevant for existing or future DIS accelerators (like EIC or LeHC) one needs to know how large are the next-to-leading order (NLO) corrections. In addition, the NLO corrections define the scale of the running-coupling constant in the BK equation and therefore determine the magnitude of the leading-order cross sections. To obtain then the structure function for DIS off a large nucleus at the NLO accuracy in $\alpha_s$, we calculate the NLO contribution to the BK equation and the NLO photon impact factor, related to the probability of the virtual photon to split in a quark anti-quark pair before scattering off the target. We obtain for the first time an analytic expression in coordinate space of the NLO photon impact factor.
Speaker: Giovanni Antonio Chirilli (Lawrence Berkeley National Laboratory (LBNL))
• 5:00 PM
Coffee break Foyer (Imperial Palace)

### Foyer

#### Imperial Palace

Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00
• Correlations and fluctuations Rotonde de l'Europe (Imperial Palace)

### Rotonde de l'Europe

#### Imperial Palace

Convener: Thomas Hemmick (SUNY Stony Brook)
• 41
Two-pion Bose-Einstein correlations in PbPb collisions at 2.76 TeV with ALICE
We present the first measurement of pion source radii in Pb-Pb collisions at the LHC. The radii were obtained by analyzing the Bose-Einstein enhancement in two-pion correlation functions. Like at lower energies, the radii drop with increasing transverse momentum, indicating the presence of collective expansion. In absolute terms, all three radii (R_out, R_side, R_long) are larger than at RHIC, roughly consistent with a linear scaling with the cube root of the particle multiplicity. The results, taken together with those obtained from the study of the multiplicity and the azimuthal anisotropy, indicate that the fireball formed in nuclear collisions at the LHC is hotter, lives longer, and expands to a larger size as compared to lower energies.
• 42
Measurements of Bose-Einstein correlations at LHC with CMS
Bose--Einstein correlations between identical particles are measured in samples of proton-proton collisions at 0.9 and 7 TeV centre-of-mass energies, recorded by the CMS experiment at the LHC. The signal is observed in the form of an enhancement of number of pairs of same-sign charged particles with small relative momentum. The dependence of this enhancement on kinematic and topological features of the event is studied.
• 43
K0sK0s correlations in 7 TeV proton+proton collisions from the ALICE experiment at the LHC
Identical neutral kaon pair correlations are measured in 7 TeV proton+proton collisions in the ALICE experiment. Neutral kaons are identified from their decay into π+π- pairs. K0sK0s correlation functions are formed in 4 multiplicity x 4 kT bins. The kaon source parameters Rinv and λ are extracted from these correlation functions by fitting a Gaussian*PYTHIA model to them, the Gaussian describing the Bose effect and PYTHIA accounting for the non-flat baseline found in proton+proton collisions. PYTHIA with the Perugia-0 tune is seen to describe well the dependence of the baseline shape of the K0sK0s correlation function on multiplicity-kT bin in the Qinv fitting range used of 0-1 GeV. Corrections to source parameters from the Lednicky model for the a0/f0 resonance are made and found to be large. K0sK0s correlations show a systematic increase in Rinv for increasing multiplicity bin and decreasing Rinv for increasing kT bin as seen in ππ correlations in the proton+proton system, as well as seen in heavy-ion collisions. Also, K0sK0s correlations are observed to more or less “smoothly” extend this ππ Rinv behavior for the proton+proton system to ~3 times higher kT than the kT range measured in ππ correlations.
Speaker: Prof. Thomas Humanic (Relativistic Heavy Ion Group, Department of Physics - Ohio State U.)
• 44
Hydrokinetic predictions for femtoscopy scales in A+A collisions in the light of recent ALICE LHC results
A study of energy behavior of the pion spectra and interferometry radii is carried out for the SPS, RHIC and LHC energies within the hydrokinetic approach. The main mechanisms that lead to the paradoxical, at first sight, dependence of the femtoscopy scales on a collision energy, in particular, a decrease of Rout/Rside ratio with the energy growth, are exposed. The hydrokinetic predictions for the HBT radii at the LHC energies are compared with the recent results of the ALICE experiment. The role of non-equilibrium stage of the matter evolution in the formation of femtoscopy scales at the LHC energies is analyzed. The results are based on: 1. Iu.A. Karpenkov, Yu.M. Sinyukov. Energy dependence of pion interferometry scales in ultra-relativistic heavy ion collisions. Phys. Lett. B 688 50 (2010). 2. Yu.M. Sinyukov, Iu.A. Karpenkov. Hydrokinetic predictions for femtoscopy scales in A+A collisions in the light of recent ALICE LHC results. arXiv:1103.5632v1 [nucl-th] 29 Mar 2011. 3. Very new results based on the Hybrid Hydrokinetic Model (not published yet).
Speaker: Prof. Yuriy Sinyukov (Bogolyubov Institute for Theoretical Physics)
• 45
Correlations and fluctuations from lattice QCD
We present the new results of the Wuppertal-Budapest lattice QCD collaboration on flavor diagonal and non-diagonal quark number susceptibilities with 2+1 staggered quark flavors, in a temperature regime between 120 and 500 MeV. A Symanzik improved gauge and a stout-link improved staggered fermion action is utilized; the light and strange quark masses are set to their physical values. Lattices with N_t=6,8,10,12 are used.
Speaker: Dr Claudia Ratti (Torino University)
• 46
Relativistic theory of hydrodynamic fluctuations
Hydrodynamic fluctuations have been applied to a wide variety of physical, chemical, and biological phenomena in the past decade. In the context of high energy heavy ion collisions, there will be intrinsic fluctuations due to the finite size and finite particle content even if the initial conditions are fixed. We develop the theory of relativistic fluctuations, and apply it to a 1+1 dimensional boost invariant model. In analogy to the cosmic microwave background radiation, fluctuations might provide information on the equation of state, including a possible critical point, and on the transport coefficients.
Speaker: Prof. Joseph Kapusta (University of Minnesota)
• Global and collective dynamics Salle de l'Europe (Imperial Palace)

### Salle de l'Europe

#### Imperial Palace

Convener: Paul Romatschke (FIAS Frankfurt)
• 47
The QGP shear viscosity: elusive goal or just around the corner?
The last two years have seen tremendous progress in the theoretical tools for extracting the specific shear viscosity of the quark-gluon plasma in the temperature range explored by heavy-ion collisions at RHIC and LHC. The effects of viscosity on the transverse momentum spectra and differential elliptic flow and their interplay with other hydrodynamic parameters have been studied systematically [1]. A global viscous hydrodynamic fit to charged and identified hadron spectra and elliptic flow at all collision centralities in RHIC Au+Au collisions has been shown to successfully extrapolate to Pb+Pb collisions at the LHC [2], providing a rather good first description of the elliptic flow measured by the ALICE collaboration. Viscous relativistic hydrodynamics has been coupled to a microscopic description of the late hadronic rescattering and freeze-out stage [3,4], thus eliminating previous large uncertainties arising from strong dissipative effects in the hadronic phase [5] and allowing for a first tightly constrained extraction of the QGP shear viscosity from RHIC data [3,6]. The largest remaining uncertainty arises from poor theoretical control over the initial spatial eccentricity of the collision fireball, and a lack of prospects to more tightly constrain this initial deformation theoretically appears to make progress towards further increased empirical precision for the QGP shear viscosity elusive. Recent studies of higher harmonic eccentricity and flow coefficients [7] and their fluctuations from collision to collision using event-by-event hydrodynamics provide, however, a novel angle that may allow to settle this question experimentally. This will be the main focus of my talk. [1] Chun Shen, U. Heinz, P. Huovinen, H. Song, Phys. Rev. C82, 054904 (2010). [2] Chun Shen, U. Heinz, et al., "Radial and elliptic flow in Pb+Pb collisions at the Large Hadron Collider from viscous hydrodynamics,'' to be published. [3] H. Song, S. A. Bass, U. Heinz, T. Hirano and Chun Shen, arXiv:1011.2783. [4] H. Song, S. Bass and U. Heinz, Phys. Rev. C, in press [arXiv:1012.0555]. [5] Chun Shen and U. Heinz, arXiv:1101.3703 [6] H. Song, S. Bass, U. Heinz, T. Hirano and Chun Shen, arXiv:1101.4638 [nucl-th]. [7] Zhi Qiu and U. Heinz, "Event-by-event shape and flow fluctuations in RHIC fireballs,'' to be published.
Speakers: Chun Shen (Ohio State University), Ulrich Heinz (The Ohio State University)
• 48
Charged hadron azimuthal anisotropy (v_2) in $sqrt s_{NN} = 2.76$ TeV PbPb collisions from CMS
During the past decade, azimuthal correlation measurements have played a pivotal role in our understanding of the properties of high density QCD matter through their sensitivity to the early stage evolution of relativistic heavy-ion collisions. Despite our increased understanding of the transport coefficients of the plasma produced in these collisions, there remain many questions concerning the interplay between initial state conditions, the equation of state, and the evolution of the system through the final hadronization stage. Detailed experimental data obtained for the energy regime accessible using the LHC should help in establishing the shear viscosity to entropy ratio achieved in the produced, strongly interacting matter. The CMS experiment has measured the anisotropy parameter, v2, using four different methods: the event-plane, two or four particle cumulants, and Lee-Yang Zeros. Consistent results are found for the different methods after considering their respective sensitivities to non-flow correlations and event-by-event fluctuations in the initial conditions. The anisotropy is studied as a function of transverse momentum, pseudorapidity and centrality in a broad kinematic range: $0.3 < p_{T} < 12.0$GeV/$c$, $|\eta|$ < 2.4, and in 12 centrality classes in the range 0-80\%. The scaling of $v_{2}$ with participant eccentricity and transverse particle density is examined and compared to lower energy results.
Speaker: Victoria Zhukova (University of Kansas)
• 49
Elliptic and triangular flow of identified particles measured with the ALICE detector.
The anisotropic flow of identified particles is an important observable to test the collective behavior of the matter created in heavy-ion collisions. We report on the first measurements of elliptic and triangular flow for charged pions, kaons and protons in lead-lead collisions at 2.76 TeV per nucleon pair center of mass energy, measured with the ALICE detector at the LHC. We will make a detailed comparison of the observed mass splitting of v_{2} at LHC energies to RHIC measurements at lower energies. For identified particles with intermediate transverse momenta we test the quark coalescence picture with v_{2} and v_{3} scaled by the number of constituent quarks vs scaled p_{t} and scaled m_{t}.
Speaker: Mikolaj Krzewicki (NIKHEF)
• 50
PHENIX measurements of higher-order flow harmonics in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV: implications for Initial-eccentricity models and the specific viscosity of the Quark Gluon Plasma
The higher-order flow harmonics $v_n$ can provide constraints crucial for precision extraction of the specific shear viscosity eta/s, of the plasma (QGP) produced in full energy ($\sqrt{s_{NN}}=200$ GeV) Au+Au collisions at RHIC. It can also provide reliable estimates of the flow correlations which contribute to the underlying event for jet-driven two-particle azimuthal angle correlation studies; the latter is important to the development of a quantitative understanding of the opacity of the QGP. Thus, significant recent attention has been given to theoretical studies of $v_n$ (odd and even) and the associated initial [fluctuating] eccentricities which drive $v_n$. In recent experiments, the PHENIX Collaboration has made detailed differential measurements of $v_n$ (odd and even) relative to the participant event planes $\Psi_n$, as well as measurements of the correlations between different $\Psi_n$ planes. The results from these measurements will be presented. Comparisons to LHC data and hydrodynamical calculations will be shown as appropriate. We will also discuss the detailed implications of these measurements for (i) improved precision for separating the flow and jet-driven contributions to $\Delta\Phi$ correlation functions, (ii) distinguishing between the two leading eccentricity models, and (iii) a more constrained estimate of $\eta/s$.
Speaker: Prof. Roy Lacey (Stony Brook University)
• 51
Event anisotropy $v_{2}$ of identified hadrons and light nuclei in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5 and 39 GeV with STAR
The main goal of the RHIC Beam Energy Scan (BES) is the exploration of the QCD phase diagram in the region of a possible phase transition between the Quark Gluon Plasma (QGP) and the hadron gas phase. In the year 2010 the first part of the BES program was successfully accomplished by recording data from Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5 and 39 GeV. The second harmonic ($v_2$) of the azimuthal particle distribution relative to the reaction plane was found to be one of the most important observables to study the underlying dynamics in the early stage of the collisions. The number-of-constituent quark (NCQ) scaling of $v_{2}$ is interpreted as a signature of deconfinement and existence of the QGP phase. At the lower energies studied it was expected to see a change in this scaling behaviour as the role of the QGP phase should diminish. We present $v_{2}$ measurements at all three beam energies for identified hadrons ($\pi$, $K$, K$_{s}^{0}$, p, $\phi$, $\Lambda$, $\Xi$) and light nuclei (d and $^{3}He$) as a function of $p_{T}$ for various collision centralities. The measured nuclei $v_{2}$ are compared to the proton $v_{2}$ and results from a dynamical coalescence model calculation, while the NCQ scaling is tested using all identified hadrons. For the first time, a significant difference in $v_{2}$ between baryons and anti-baryons is observed. The difference increases with decreasing center-of-mass energy.
Speaker: Dr Alexander Schmah (Lawrence Berkeley National Lab)
• 52
Sensitivity of the elliptic flow coefficient to a temperature-dependent shear viscosity-to-entropy density ratio in ultrarelativistic heavy-ion collisions at RHIC and LHC
We investigate the effects of a temperature-dependent shear viscosity-to-entropy density ratio $\eta/s$ on the elliptic flow of hadrons in ultrarelativistic heavy-ion collisions [1]. We use relativistic dissipative fluid dynamics to model the space-time evolution of the hot and dense system formed in such collisions. The final hadron spectra are calculated using the Cooper-Frye freeze-out procedure. By studying different parametrizations for the temperature dependence of $\eta/s$, we found that the viscous suppression of the elliptic flow coefficient in $\sqrt{s_{NN}} = 200$ GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) is dominated by the viscosity in the hadronic phase and in the phase transition region. However, the elliptic flow at RHIC is largely insensitive to the viscosity of the quark-gluon plasma (QGP). On the other hand, we found that sensitivity of the elliptic flow to the high-temperature $\eta/s$ increases with increasing multiplicity and simultaneously the sensitivity to the hadronic viscosity decreases. At the highest LHC energy, the elliptic flow becomes sensitive to the QGP viscosity and insensitive to the hadronic viscosity. The change of the sensitivity from hadronic to QGP viscosity from RHIC to LHC can provide access to determining the temperature dependence of $\eta/s$ from elliptic flow data. [1] H. Niemi, G. S. Denicol, P. Huovinen, E. Molnar, D. H. Rischke, [arXiv:1101.2442 [nucl-th]].
Speaker: Dr Harri Niemi (Frankfurt Institute for Advanced Studies)
• Hadron thermodynamics and chemistry Salon Haendel AB (Imperial Palace)

### Salon Haendel AB

#### Imperial Palace

Convener: Jan Rak (Helsinki Institute of Physics HIP)
• 53
K0s and Lambda production in PbPb collisions with the ALICE experiment
We present the study of K0s and Lambda production performed with the ALICE experiment at the LHC in Pb-Pb collisions at sqrt(sNN)=2.76 TeV and pp collisions at sqrt(s)=0.9 and 7 TeV. The K0s and Lambda particles are reconstructed via their V0 decay topology allowing their identification up to high transverse momenta. The corresponding baryon/meson ratios as a function of transverse momentum are extracted for Pb-Pb collisions in centrality bins and in the transverse momentum range from 1 to 10 GeV/c. They are also compared with the ones measured in pp events at the LHC energies of 0.9 and 7 TeV as well as in Au-Au collisions at sqrt(sNN)=0.2 TeV from RHIC.
Speaker: Iouri BELIKOV (IPHC, CNRS-IN2P3)
• 54
Multi-strange particle measurements in 7 TeV proton-proton and 2.76 TeV PbPb collisions with the ALICE experiment at the LHC
The production of charged multi-strange particles is studied with the ALICE experiment at the CERN LHC. Measurements of the central rapidity yields of $\Xi^{-}$ and $\Omega^{-}$ baryons, as well as their antiparticles, are presented as a function of transverse momentum ($p_{T}$) for inelastic pp collisions at $\sqrt{s}=7\:TeV$ and compared to existing measurements performed at the same and/or at lower energies. The results are also compared to predictions from PHOJET and several tunes of the PYTHIA event generators. We find that data significantly exceed the production rates from those models, everywhere except potentially for high $p_{T}$, where hard QCD processes dominate. Finally, we present the status of the multi-strange particle production studies in Pb-Pb at $\sqrt{s}=2.76\:TeV$ performed as a function of collision centrality.
Speaker: D.D. Chinellato (Instituto de Fisica Gleb Wataghin (IFGW) - Universidade Estadual de Campinas)
• 55
High-pT suppression of Lambda and K0s in PbPb collisions at sqrt(sNN) = 2.76 TeV with ALICE
Significant suppression of unidentified charged particles at large transverse momentum has been observed in central Pb-Pb collisions at the LHC. Measurements of identified particles will provide more detailed information on the suppression mechanism. The production of Lambda and K0s at mid-rapidity in pp and Pb-Pb at sqrt(sNN) = 2.76 TeV is studied with the ALICE detector at the LHC. Lambda and K0s are measured by reconstructing their weak decays into charged hadrons, employing the tracking capabilites of the ALICE central barrel. The analysis of Lambda and K0s production in Pb-Pb is performed in intervals of the collision centrality and compared to results from pp at the same collision energy. We discuss the centrality dependence with particular emphasis on strange particle suppression at high pT.
Speaker: Simone Schuchmann (Institut fuer Kernphysik-Johann-Wolfgang-Goethe Univ.)
• 56
The thermal model on the verge of the ultimate test: the LHC data
In our model, both the light (u,d,s) quark sector and charm(onium) have found a unified description, thus providing very different probes for a possible delineation of the phase boundary between deconfined and hadronic matter produced in nucleus-nucleus collisions from low (AGS) energies up to RHIC energy. A purely thermal production (at chemical freeze-out) appears natural for u,d,s-carrying hadrons and a good degree of consensus has been achieved with the RHIC data, at least for central collisions. We are rather confident in predicting the chemistry of ligh-quark hadrons at the LHC. In contrast, charmed hadrons and charmonia can be produced at chemical freeze-out only as a result of a "distribution" into hadrons of charm quarks produced in primary hard collisions. Our model describes rather well the RHIC and SPS data on charmonia, which will be reviewed briefly. We expect that generation at the phase boundary is at the LHC the exclusive mechanism (thus lifting the present controversy whether charmonia melt or not in the deconfined stage at RHIC and SPS energies). With some of the model ingredients (like the volume at chemical freeze-out) already constrained by the first LHC data, the main uncertainty in our predictions remains the charm cross section in Pb-Pb, where shadowing is not yet known. In addition to the overall hadron abundancies, including those of light (hyper)nuclei and their antiparticles, we provide predictions for charmonia and for charmed hadrons, to be confronted soon with the LHC data.
Speaker: Dr Anton Andronic (Gesellschaft fuer Schwerionenforschung mbH (GSI))
• 57
Measurement of light vector mesons by PHENIX experiment at RHIC
The PHENIX experiment at RHIC has carried out systematic measurements of $\phi$ and $\omega$ mesons in $p+p$, $d+Au$, $Cu+Cu$ and $Au+Au$ collisions at $\sqrt{s_{NN}}$ = 200 GeV. Consistent results have been obtained using leptonic and hadronic decay modes as well as different analysis techniques. In $p+p$ collisions, the transverse momentum distributions of $\omega$ and $\phi$, as well as all other mesons measured by PHENIX, are well described by the Tsallis distribution functional form. Combining the $e^+e^-$ and hadronic ($\omega \rightarrow \pi^0 gamma,~\pi^0\pi^+\pi^-$, $\phi \rightarrow K^+K^-$) decay channels, $\omega$ and $\phi$ have been measured over a $p_T$ range of 0 - 13.5 GeV/c and 0 - 7 GeV/c respectively. New results obtained using hadronic and dielectron channels of $\omega$ and $\phi$ mesons in $d+Au$ collisions extend the $p_T$ coverage to 0.25 - 13 GeV/c and 0 - 7 GeV/c respectively, and reveal a moderate enhancement at intermediate $p_T$ and a hint of suppression at $p_T >$ 8 GeV/c. Both observations are consistent with previous results for $\pi^0$, $\pi^+ + \pi^-$, $K_s$ and $K^+ + K^-$. The nuclear modification factor of $\omega$ in $Cu+Cu$ and $Au+Au$ collisions measured over a $p_T$ range of 4 - 12 GeV/c, shows that $\omega$ has a similar suppression pattern as that of $\pi^0$ and $\eta$, strengthening the observation that mesons with different masses have similar behavior but different from the one of baryons. However, $\phi$ in $Cu+Cu$ and $Au+Au$ collisions, measured from 1 - 7 GeV/c, shows a suppression, that is smaller than that of the $\pi^0$ and $\eta$ in the intermediate $p_T$ range (2 - 5 GeV/c), whereas at higher $p_T$, within the large experimental uncertainties, the amount of suppression appears similar to that of the light mesons. Results of $\phi$ production at $\sqrt{s_{NN}}$ = 62.4 GeV show a similar behavior but with larger uncertainties. This talk will review the most recent results obtained for light vector mesons in different collision systems and energies.
Speaker: Dr Deepali Sharma (Weizmann Institute of Science)
• 58
Vector meson production in pp collisions at sqrt(s)=7 TeV, measured with the ALICE detector
Low mass meson ($\rho^0, \omega, \phi$) production provides key information on the hot and dense state of strongly interacting matter produced in high-energy heavy ion collisions. Among them, strangeness enhancement can be accessed through the measurement of $\phi$ meson production, while the measurement of the $\rho$ spectral function can be used to reveal in-medium modifications of hadron properties close to the QCD phase boundary. Vector meson production in pp collisions provides a reference for these studies. Moreover, it is interesting by itself, since it can be used to tune particle production models at the unexplored LHC energy range. The ALICE experiment at the LHC can access vector mesons produced at forward rapidity through their decays in muon pairs, and at central rapidity in the di-electron decay channel. We present transverse momentum spectra of $\phi$ and $\rho$+$\omega$ mesons at forward rapidity in pp collisions at $\sqrt{s}=7$~TeV, as well as the $\phi$ absolute production cross section. We will also discuss the first signals and the analysis prospects for vector meson studies at forward rapidity in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$~TeV.
Speaker: Alessandro De Falco (Univ. + INFN Cagliari)
• Heavy flavor Salon Ravel AB (ImpErial Palace)

### Salon Ravel AB

#### ImpErial Palace

Convener: Enrico Scomparin (INFN, Torino)
• 59
STAR measurements of bottom to charm ratio and heavy quark interaction with the QCD medium through non-photonic electron-hadron correlations
FOR THE STAR COLLABORATION Heavy Quarks are mostly produced through gluon fusions during the initial stage of the heavy ion collisions. Experimentally heavy quarks are found to suffer a considerable energy loss in the QCD medium with the nuclear modification factor for non-photonic electrons (NPE) from heavy quark decays much smaller than unity in central Au+Au collisions at RHIC. To better understand the heavy flavor production and energy loss mechanism it is crucial to determine experimentally the relative contributions of Charm and Bottom meson decays to NPE and to study detailed characteristics of heavy quark interactions with the bulk QCD medium. We will present the STAR measurements of relative charm and bottom contributions to NPE from p+p collisions at 200 and 500 GeV energies. We report the total bottom quark production cross section from p+p collisions at 200 GeV extracted from NPE spectrum and B to D ratios. We will also present the NPE-hadron correlations from Au+Au collisions at 200 GeV from the 2010 RHIC run where we have collected high statistics data set with low photonic conversion background. The evolution of the NPE-hadron azimuthal angular correlation as a function of collision centralities and in comparison with that from d+Au collisions will be indicative of dynamics of heavy quark interactions with the QCD medium created in Au+Au collisions. Comparisons with theoretical calculations will also be discussed.
Speaker: wenqin xu (University of California Los Angeles)
• 60
Open heavy flavor physics in the muon channel with ALICE in pp collisions at 7 TeV and PbPb at 2.76 TeV
Heavy-quark production is one of the probes for the investigation of the properties of the high-density medium formed in heavy-ion collisions. This investigation requires also the study of proton-proton collisions. Besides providing the necessary baseline for nucleus-nucleus collisions, proton-proton collisions are of great interest, also in their own right, since they allow to test perturbative QCD at unprecedented low Bjorken-x values. In this contribution, we measure the heavy-flavour production by detecting single muons from semi-leptonic decays. After a description of the ALICE muon spectrometer, we will present the results on the production of single muons from heavy flavour decays at forward rapidity (2.5 < y < 4) in pp collisions at Heavy-quark production is one of the probes for the investigation of the properties of the high-density medium formed in heavy-ion collisions. This investigation requires also the study of proton-proton collisions. Besides providing the necessary baseline for nucleus-nucleus collisions, proton-proton collisions are of great interest, also in their own right, since they allow to test perturbative QCD at unprecedented low Bjorken-x values. In this contribution, we measure the heavy- avour production by detecting single muons from semi-leptonic decays. After a description of the ALICE muon spectrometer, we will present the results on the production of single muons from heavy avour decays at forward rapidity (2:5 < y < 4) in pp collisions at √s = 7 TeV and Pb-Pb collisions at Heavy-quark production is one of the probes for the investigation of the properties of the high-density medium formed in heavy-ion collisions. This investigation requires also the study of proton-proton collisions. Besides providing the necessary baseline for nucleus-nucleus collisions, proton-proton collisions are of great interest, also in their own right, since they allow to test perturbative QCD at unprecedented low Bjorken-x values. In this contribution, we measure the heavy- avour production by detecting single muons from semi-leptonic decays. After a description of the ALICE muon spectrometer, we will present the results on the production of single muons from heavy avour decays at forward rapidity (2:5 < y < 4) in pp collisions at √s = 7 TeV and Pb-Pb collisions at √sNN = 2.76 TeV. In particular, we will show the pt-dierential production cross section in pp collisions and compare it to perturbative QCD predictions, and the nuclear modication factors in Pb-Pb collisions. RAA with respect to a pp reference at √s = 2.76 TeV and RCP in central with respect to peripheral collisions.
Speaker: Xiaoming Zhang (Laboratoire de Physique Corpusculaire, Clermont-Ferrand)
• 61
Quark recombination and heavy quark diffusion in hot nuclear matter
We review resonance recombination for quarks and show that it is compatible with quark and hadron distributions in local thermal equilbrium. We then calculate realistic heavy quark phase space distributions in heavy ion collisions using Langevin simulations with non-perturbative interactions in hydrodynamic backgrounds. We hadronize the heavy quarks on the critical hypersurface given by hydrodynamics after constructing a criterion for the relative recombination and fragmentation contributions. We discuss the influence of recombination and flow on the resulting heavy meson and single electron R_AA and elliptic flow. We will also comment on the effect of diffusion of open heavy flavor mesons in the hadronic phase.
Speaker: Prof. Rainer Fries (Texas A&M University + RBRC)
• 62
Heavy-flavor production cross section in the semi-electronic channel at mid-rapidity in pp collisions at sqrt(s)=7 TeV with ALICE
Heavy quarks (charm and beauty) are among the most important probes that allow to test perturbative QCD descriptions of hard processes in hadronic interactions, as well as to study the hot matter produced in high energy nucleus-nucleus collisions. Precision measurements of heavy flavour production in proton-proton collisions provide the necessary reference for the interpretation of their behaviour in the deconfined state of strongly-interacting matter (Quark-Gluon Plasma). Both collision systems can be extensively studied with ALICE at LHC. The production of heavy quarks can be measured via the detection of their semileptonic decays. We present the measurement of the inclusive electron spectrum at mid-rapidity, in proton-proton collisions and sqrt(s)=7 TeV, based on the excellent particle identification capabilities of ALICE. The statistical subtraction of a cocktail that accounts for photonic electrons and other background sources, built on the base of ALICE measured meson spectra, provides a measurement of the production cross section of electrons from heavy-flavour hadron decays. The further subtraction of the charm component, obtained from the D meson cross section measured by ALICE in the same rapidity range, as well as an analysis of impact parameter distributions relative to the interaction vertex, allow to determine the electron spectrum from pure beauty decays. The results will be presented, compared to theoretical predictions, and discussed in the perspective of obtaining a reference for the studies of heavy quark energy loss in the Quark-Gluon Plasma.
Speaker: Dr Silvia Masciocchi (GSI Darmstadt)
• 63
Heavy quark diffusion from lattice QCD spectral functions
We analyze the low energy part of charmonium spectral functions on large lattices close to the continuum limit in the temperature region $1.5 Speaker: Dr Heng-Tong Ding (Brookhaven National Lab) • 64 Bottomonium production measured in PbPb and pp collisions by CMS The LHC centre-of-mass energy allows copious$\Upsilon$production in PbPb collisions. Detailed measurements of bottomonium will help characterize the dense matter produced in heavy-ion collisions beyond what was accessible at RHIC (mostly) with charmonia. The full spectroscopy of quarkonium states has been suggested as a possible thermometer for the QGP. With its excellent dimuon mass resolution, CMS has measured the three$\Upsilon$states in pp collisions. With the 2010 PbPb data sample, CMS has observed the$\Upsilon$. The$\Upsilon(1S)$cross-section is presented as a function of transverse momentum, rapidity and centrality. Speaker: Zhen Hu (Purdue University) • Tuesday, May 24 • Pre equilibrium and initial stage and global collective dynamics Théâtre National ### Théâtre National #### Centre Bonlieu 1 Rue Jean Jaurès, 74000 Annecy, France Tel : +33 4 50 45 00 33 Convener: Bernd Mueller (Duke University) • 65 Initial conditions - Theory perspectives Speaker: Javier Lopez Albacete (IPhT CEA/Saclay) • 66 Bulk properties of PbPb collisions at the LHC measured by ALICE Global variables, such as the charged particle multiplicity and the transverse energy are important observables to characterize Relativistic Heavy Ion collisions and to constrain model calculations. The charged-particle multiplicity dNch/deta(eta=0) and transverse energy dEt/deta(eta=0) are measured at sqrt(s_NN)=2.76TeV in Pb-Pb collisions as a function of centrality and in p-p collisions. The fraction of inelastic cross section seen by the ALICE detector is calculated either using a Glauber model or the data corrected by simulations of nuclear and EM processes, or data collected with a minimum bias interaction trigger. The centrality, defined by the number of nucleons participating in the collision, is obtaine, via the Glauber model, by relating the multiplicity distributions of various detectors in the ALICE Central Barrel and their correlation with the spectator energy measured by the Zero-Degree Calorimeters. The results are compared to corresponding results obtained at the significantly lower energies of the BNL AGS, the CERN SPS, and the BNL RHIC, and with models based on different mechanisms for particle production in nuclear collisions. Particular emphasis will be given to a discussion on systematic studies of the dependence of the centrality determination on the Glauber model, and the validity of the Glauber model at unprecedented collision energies. Speaker: Dr Alberica Toia (Organisation européenne pour la recherche nucléaire (CERN)) • 67 Femtoscopy of PbPb and pp collisions at the LHC with the ALICE experiment We report on the results of femtoscopic analysis of Pb-Pb collisions at$\sqrt{s_{NN}}=2.76$~TeV with identical pions and pp collisions at$\sqrt{s}=0.9$,$2.76$and$7$~TeV with identical pions and kaons. Detailed femtoscopy studies in heavy-ion collisions at SPS and RHIC have shown that emission region sizes ("HBT radii") decrease with increasing pair momentum, which is understood as a manifestation of the collective behavior of matter. The trend was predicted to persist at the LHC. The data from Pb-Pb collisions confirm the existence of a flowing medium and provide strict constraints on the dynamical models. Similar analysis is carried out for pp collisions for pions and kaons and qualitative similarities to heavy-ion data are seen, especially in collisions producing large number of particles. The observed trends give insight into the soft particle production mechanism in pp collisions. 3D radii were also found to universally scale with event multiplicity in heavy-ion collisions. We extend the range of multiplicities both upwards with the Pb-Pb data and downwards with the pp data to test the scaling in new areas. In particular the high multiplicity pp collisions reach particle densities comparable to the ones measured in peripheral Cu-Cu and Au-Au collisions at RHIC. This allows for the first time to directly compare freeze-out sizes for systems with very different initial states. Speaker: Adam Kisiel (CERN) • 68 Common discussion with 3 speakers Speaker: Bernd Mueller (Duke University) • 9:50 AM Coffee break Théâtre National ### Théâtre National #### Centre Bonlieu France • Global collective dynamics Théâtre National ### Théâtre National #### Centre Bonlieu 1 Rue Jean Jaurès, 74000 Annecy, France Tel : +33 4 50 45 00 33 Convener: Ulrich Heinz (MPS) • 69 Flow - Theory perspective Speaker: Björn Schenke (Brookhaven National Laboratory) • 70 Collective flow measurements from the PHENIX Experiment Recent collective flow measurements including higher moment event anisotropy from the PHENIX experiment will be presented, the particle type, beam energy dependence and the relation with jet modification will be discussed. Speaker: Shinichi Esumi (Institute of Physics - University of Tsukuba) • 71 Flow measurements from the CMS experiment We report on the CMS measurements of charged hadron anisotropic azimuthal distributions from PbPb collisions at √sNN= 2.76 TeV and their decomposition into a Fourier series up to the 6th coefficient. The results are presented as a function of transverse momentum, centrality and pseudorapidity and cover a broad kinematic range. The relation between the different harmonic coefficients and the scaling with the respective participant eccentricity are studied. These results could provide constraints on the theoretical description of the early dynamics in the hot and dense medium and its transport properties. Speaker: Julia Velkovska (Vanderbilt University) • 72 ATLAS flow Speaker: Jiangyong Jia (Brookhaven National Laboratory (BNL)- Stony Brook University) • 73 Anisotropic flow from ALICE We report on the measurements of anisotropic flow with the ALICE detector at the LHC. For charged particles we present the first triangular, quadrangular and pentagonal flow measurements. The flow of charged and identified particles is compared to hydrodynamic model predictions at low-p_t and for identified particles at intermediate-p_t the so-called number of constituent quark scaling is investigated. At higher transverse momentum we compare the elliptic flow results with expectation from parton energy loss. For the integrated elliptic flow we show the scaling with the initial eccentricity and we quantify the magnitude of the event by event fluctuations. These results indicate strong collective flow and are consistent with expectations for the created hot and dense system created at the LHC. Speaker: Raimond Snellings (Nikhef, Amsterdam,The Netherlands) • 74 Common discussion with 4 experimental speakers Speaker: Ulrich Heinz (Ohio State University) • Zimanyi Nuclear Theory Medal Théâtre National ### Théâtre National #### Centre Bonlieu France • 12:45 PM Lunch break Restaurant La Voile, Brasserie du Parc/Rotonde du Parc (Imperial Palace) ### Restaurant La Voile, Brasserie du Parc/Rotonde du Parc #### Imperial Palace La Voile 200 + Brasserie 500 • Correlations and fluctuations Rotonde de l'Europe (Imperial Palace) ### Rotonde de l'Europe #### Imperial Palace Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Convener: Guy Paic (Universidad Nacional Autonoma de Mexico (UNAM)) • 75 Triggered di-hadron correlations in PbPb collisions from the ALICE experiment Angular correlations between unidentified hadron trigger and associated particles are measured by the ALICE experiment for$0.5 < p_{t}^{(t),(a)} < 15$GeV/c, where$p_t^{(t)} > p_t^{(a)}$. The modification of conditional yields in central Pb--Pb collisions is measured with respect to p--p ($I_{AA}$) and with respect to peripheral events ($I_{CP}$). Significant suppression is observed on the side opposing the trigger, while an enhancement is measured on the near side. The latter result is a notable departure from RHIC measurements. In addition, the shape of the pair azimuthal distribution is examined in a variety of centrality categories for pairs in$|\eta| < 0.8$where$|\eta^{(t)} - \eta^{(a)}| > 0.8$. A set of two-particle Fourier components$V_{n\Delta} \equiv \langle \cos(n\Delta\phi)\rangle$are computed directly from the long-range azimuthal correlation functions. A series including$V_{1\Delta}$to$V_{5\Delta}$describes the data. For each$n$, a fit is applied over all$p_{T}$bins simultaneously to test the collectivity hypothesis$V_{n\Delta} \simeq v_n^{(t)} \, v_n^{(a)}$. This factorization hypothesis is satisfied at low$p_{T}$but not at higher$p_{T}$. The divergence between the data and the global fit provides a new measure of the onset of nonflow dominance in long-range correlations due to the away side jet. The first five single-particle$v_n$coefficients are presented as new results from the global fit, and are compared to$v_n$values measured by more established methods. Speaker: Dr Andrew Adare (Yale University) • 76 Dihadron correlations in PbPb collisions at$\sqrt{s_{_{NN}}}$= 2.76 TeV with CMS Measurements of charged dihadron correlations from the CMS collaboration are presented for PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair over a broad range of pseudorapidity and the full range of azimuthal angle. With its large pseudorapidity coverage (|$\eta$|<2.4), the CMS tracker is ideally suited for detailed analyses of both short and long-range charged hadron correlations at the LHC. For the most central 0-5\% collisions, a broadening of the away side ($\Delta\phi>1$) dihadron correlation is observed at all$\Delta\eta$when compared to pp collisions. A significant correlated yield is observed for pairs of particles with small$\Delta\phi$but large longitudinal separation$\Delta\eta$, commonly known as the `ridge''. The ridge persists up to at least$|\Delta\eta| = 4$and its effect is found to be stronger than what was previously observed at RHIC. The dependence of the ridge region shape and yield on transverse momentum and collision centrality has been measured. For particles of transverse momentum of 2--4 GeV/$c$, the ridge is found to be the most prominent when correlated to particles of 2--6 GeV/$c$, but disappears when correlated to 8--10 GeV/$c$particles. A Fourier analysis of the long-range two-particle correlations will be presented and discussed in the context of CMS measurements of higher order flow coefficients. Speaker: Jeremy Louis Callner (Physics Department-University of Illinois at Chicago) • 77 Untriggered di-hadron correlations in PbPb \sqrt{s_{NN}} =2.76 TeV collisions from the ALICE experiment We present measurements of untriggered di-hadron correlations as a function of centrality in Pb-Pb \sqrt{s_{NN}} =2.76 TeV collisions, for charged hadrons with p_{T} > 0.15 GeV/c. These measurements provide a map of the bulk correlation structures in heavy-ion collisions. Contributions to these structures may come from jets, initial density fluctuations, elliptic flow, and/or momentum conservation. We will decompose the measured correlation functions via a multi-parameter fit in order to extract the soft ridge; the long range \delta(\eta) correlation on the nearside observed at RHIC energies. The effect of including higher harmonics (v_{3} and v_{4}) in this procedure will be discussed. We will compare our results to various theoretical predictions based on differing schemes for the initial conditions. Finally, we will investigate empirical scalings (such as the number of binary collisions) for the various contributions as a function of centrality, which may also help determine their origin. Speaker: Dr Anthony Timmins (University of Houston) • 78 A comprehensive study of the high-pt particle correlations in pp collisions at LHC/ALICE Two-particle correlation with the high-pT triggers allows the study of the hard scattering phenomena like soft QCD radiation [1, 2], angular ordering [3] or jet frag- mentation in the low and intermediate pT region [4, 5] where full jet reconstruction is challenging. An analysis of the first ALICE pp data where charged particle, π0 and isolated photon are used as trigger particles will be presented. These measurements will serve as a reference for the same measurements in Pb-Pb collisions. A sensitivity of the associated particle momentum projection into the direction of the trigger particle, xE = −p⃗Th± · p⃗Ttrig / | p⃗Ttrig |2, can be used to extract the average trigger particle momentum fraction and the jet imbalance function, whereas the γ-hadron correlations can be used to study the jet fragmentation function directly. The quest for the nuclear modification of the partonic properties in heavy ion collisions, using above mentioned quantities, will be also outlined. References [1] D. Boer and W. Vogelsang, Phys. Rev. D69, 094025 (2004), hep-ph/0312320. [2] R. Perez-Ramos, F. Arleo, and B. Machet, Phys. Rev. D78, 014019 (2008), 0712.2212. [3] Y. L. Dokshitzer, D. Diakonov, and S. Troian, Phys.Rept. 58, 269 (1980). [4] PHENIX, S. S. Adler et al., Phys. Rev. D74, 072002 (2006), hep-ex/0605039. [5] PHENIX Collaboration, A. Adare et al., Phys. Rev. D 82, 072001 (2010), arXiv:1006.1347. Speaker: Yaxian Mao (CCNU, Wuhan & LPSC, Grenoble) • 79 Event-by-event mean$p_{T}$fluctuations in pp and PbPb collisions measured by the ALICE experiment at the LHC Non-statistical event-by-event fluctuations of the mean transverse momentum of charged particles in pp and Pb--Pb collisions are studied using the ALICE experiment at the LHC. The analysis is performed at$|\eta| < 0.8$and$0.15 < p_{T} < 2 $~GeV/c. Multiplicity dependent results are obtained for pp collisions at$\sqrt{s}$~=~0.9, 2.76 and 7~TeV. Pb--Pb collisions at$\sqrt{s_{NN}}$~=~2.76~TeV are analysed in intervals of multiplicity and centrality, the latter in bins of 5\%. Little collision energy dependence is observed in pp collisions. The data indicate a common scaling behaviour with event multiplicity from pp to semi-central Pb--Pb collisions. In central Pb--Pb collisions, the results deviate from this trend, exhibiting a significant reduction of the fluctuation strength. The results are compared to measurements in Au--Au collisions at lower collision energies and to Monte Carlo simulations with PYTHIA and HIJING. Speaker: Stefan Heckel (Johann-Wolfgang-Goethe Univ.) • 80 New results on event-by-event ratio fluctuations in PbPb collisions at CERN SPS energies Event-by-event fluctuations of hadron ratios characterize the hadro-chemical composition of the hot and dense medium created in heavy-ion collisions. This makes the fluctuation signal sensitive to changes in the underlying structure of matter, and phase transition effects in particular. In the SPS energy range, inclusive hadronic observables indicate the onset of the deconfinement phase transition [1], making ratio fluctuations a promising observable to further characterize the transition and possibly reveal signatures of the conjectured critical point as suggested by lattice calculations of quark number susceptibilities at finite mu_B [2]. Kaons and protons carry large parts of the conserved quantities strangeness and baryon number. Their correlation, reflected in the kaon-to-proton ratio fluctuations, is expected to undergo a significant change at the anticipated parton-hadron phase boundary [3]. Results on (K+ + K−)/(p + pbar) and K+/p fluctuations in heavy-ion collisions will be presented for the first time. At 5 energies between sqrt(s_NN) = 6.3 and 17.3 GeV, sigma_dyn has been evaluated in central Pb+Pb collisions. For both ratios, a fast transition from positive sigma_dyn at low SPS energies to negative values at the higher energies is observed, an energy dependence that is not reproduced by hadronic models. While hadronic transport models predict almost constant fluctuations in the SPS energy range, a multiplicity scaling as suggested in [4] is also incompatible with the data. This study is complemented by new results on the centrality dependence of ratio fluctuations at sqrt(s_NN) = 17.3 GeV, which confirm the systematics recently reported at RHIC energies [5]. References [1] C. Alt et al. [NA49 Collaboration], Phys. Rev. C 77, 024903 (2008) [arXiv:0710.0118 [nucl-ex]]. [2] M. Cheng et al., Phys. Rev. D 79, 074505 (2009) [arXiv:0811.1006 [hep-lat]]. [3] V. Koch, A. Majumder and J. Randrup, Phys. Rev. Lett. 95, 182301 (2005) [arXiv:nucl-th/0505052]. [4] V. Koch and T. Schuster, Phys. Rev. C 81, 034910 (2010) [arXiv:0911.1160 [nucl-th]]. [5] B. I. Abelev et al. [STAR Collaboration], Phys. Rev. Lett. 103, 092301 (2009). [arXiv:0901.1795 [nucl-ex]]. Speaker: Tim Schuster (Frankfurt Institute for Advanced Studies, Goethe-University Frankfurt) • 81 Femtoscopy of the system shape fluctuations in heavy ion collisions The system created in a heavy ion collision in general is not azimuthally symmetri; moreover, the initial spatial distribution, e.g. that of the energy density, fluctuates event-by-event even at fixed impact parameter. Because of particle interactions, this initial spatial asymmetry leads to anisotropies in particle emission -- the phenomenon called anisotropic flow. The best known anisotropy of this kind is the elliptic flow that is described by the second harmonic in particle azimuthal distribution. Recently, the so-called triangular, and higher harmonic flow, and in particular their sensitivity to the system initial conditions attracted a lot of attention, as they might provide additional important information about the initial conditions and dynamical properties (e.g. viscosity) of the system. Fluctuations in the initial geometry should be also reflected in the detail shape of the system at freeze-out. In this talk I discuss the possibility to measure such fluctuations by means of identical and non-identical particle femtoscopy. I support my conclusion on the sensitivity of the method to measure triangularity and higher harmonic spatial asymmetries by analytical calculations, and by results from event generators and blast wave model calculations. Speaker: Prof. Sergei Voloshin (Department of Physics and Astronomy-College of Science-Wayne Sta) • Heavy flavors Salon Ravel AB (Imperial Palace) ### Salon Ravel AB #### Imperial Palace Convener: Julia Velkovska (Vanderbilt University) • 82 Charmonium production measured in PbPb and pp collisions by CMS CMS is fully equipped to measure hard probes in the di-muon decay channel in the high multiplicity environment of nucleus-nucleus collisions. Such probes are especially relevant for studying the quark gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. In particular, the$J\psi$production in heavy ion collisions has been studied at different energies and with different collision systems without yet giving a global picture that is fully understood. Measuring the charmonium production at the LHC energies in PbPb collisions will help constraining predictions, in particular those expecting high recombination of prompt J$/\jpsi$s or suppression in hot medium. We will review CMS J/\psi measurements in pp collisions at$\sqrt{s_{NN}}=7$~TeV, which allow precision studies of quarkonia production and serve as a reference for the observation of hot nuclear effects. CMS is able to distinguish non-prompt J$/\psi$from prompt J/$\psi$in PbPb collisions, and will present the prompt J/$\psi$production cross-section in PbPb inclusively and as a function of transverse momentum, rapidity and number of nucleons participating in the collision. Finally, we compare the B fraction measured in PbPb collisions with that measured in pp at various energies. Speaker: Torsten Dahms (LLR - Ecole Polytechnique, IN2P3-CNRS) • 83 Measurement of J/psi production at forward rapidity in pp collisions at sqrt(s)= 2.76 and 7 TeV with ALICE The ALICE experiment has studied J/psi production at forward rapidity from pT=0, through its dimuon decay channel, in proton-proton and Pb-Pb collisions at the LHC. Results obtained in proton-proton collisions at sqrt(s)=7 TeV will be discussed. The integrated and differential (in pT and rapidity) inclusive production cross sections will be presented and compared to results from other LHC experiments. First results on the J/psi integrated and differential cross sections in proton-proton collisions at sqrt(s)=2.76 TeV will also be discussed. These measurements, at the same centre-of-mass energy as for Pb-Pb collisions, provide a crucial reference for the study of nuclear matter effects on J/psi production. Speaker: Dr Roberta Arnaldi (INFN Torino) • 84 J/Psi production and correlation in p+p and R_{AA} at high-pt in Au+Au collisions The$c\bar{c}$bound state$J/\psi$provides a unique tool to probe the properties of the hot dense medium produced in heavy-ion collisions, but to date its production mechanism is not understood clearly either in heavy-ion collisions or in hadron hadron collisions. Measurement of$J/\psi$production at high$p_T$is particularly interesting since at high$p_T$the various models give different predictions. Besides, high$p_T$particles are widely used to study the parton-medium interactions in heavy-ion collisions. The previous high-$p_TJ/\psi$measurements in$p+p$and Cu+Cu collisions at RHIC published by the STAR collaboration found several interesting things, though constrained by limited statistics and system size. In this talk, we will present the new measurement of$J/\psi \rightarrow e^+e^-$production at large$p_T$range ($0< p_T< 10~\textrm{GeV}/c$) at mid-rapidity ($|y|<1$)in$p+p$and Au+Au collisions at 200 GeV. The datasets are from RHIC year 2009$p+p$and 2010 Au+Au runs with significantly reduced material, the newly installed full TOF, and high data acquisition rates.$J/\psip_T$spectra and nuclear modification factors from low to high$p_T$will be discussed to understand its production mechanism and medium modifications. The$J/\psi$-hadron azimuthal angle correlation in$p+p$collisions will be presented to disentangle$B$-mesons contributions to inclusive$J/\psi$and study J/$\psi$hadronization mechanism. Speaker: Zebo Tang (University of Science and Technology of China) • 85 Heavy quarkonium measurements from PHENIX Quarkonia suppression is one of the highly cited signature of quark gluon plasma (QGP) formed in relativistic heavy ion collisions. PHENIX observed a high suppression of$J/\Psi$production in Au+Au collisions at$\sqrt{s}=200$GeV. However, theoretical predictions remain diverse due to lack of precise knowledge of heavy flavor meson production, suppression, regeneration in hot and dense medium and other cold nuclear effects. In order to separate these effects the PHENIX collaboration also measured$J/\Psi$production in d+Au collisions at$\sqrt{s}=200$GeV for isolating cold nuclear effects and Au+Au collisions at low energies ($\sqrt{s}=62$GeV and 39 GeV) to study the onset of nuclear phase transition to QGP. The idea being that the critical energy density for a crossover into the QGP phase may not be reached for certain combinations. The measurement of$J/\Psi$nuclear modification factors at different center of mass energies may elucidate this transition and supplement our understanding of the energy dependence of cold nuclear matter effects. \\ In this talk, we will show the latest results of$J/\Psi$and Upsilon measurements from p+p, d+Au collisions at$\sqrt{s}=200$GeV and several energy scans of Au+Au collisions. Speaker: Abhisek Sen (Georgia State University) • 86 Charmonium spectral functions at finite momenta in the quark-gluon plasma from lattice QCD From phenomenological considerations, J/psi suppression was proposed as a signature of QGP production in relativistic heavy ion collisions, and has been considered as one of the most promising ones [1]. However recent lattice QCD calculations show that charmonia survive even above the critical temperature [2], which presents the possibility that the scenario of J/psi suppression in relativistic heavy ion collisions may change. To understand the relativistic heavy ion collision physics we need to take into account dynamics of the fireball which is produced after collisions. Therefore the detailed study on spectral functions of charmonia at finite momenta from the first principle calculation would shed light on the understanding of the J/psi suppression mechanism in relativistic heavy ion collisions. We study the charmonium spectral functions at finite momenta in the quark-gluon plasma on 64^3 × N_t(=96(T/Tc=0.78),54(1.38),46(1.62),40(1.87),32(2.33)) quenched anisotropic lattices with anisotropy a_s /a_t= 4, analyzing correlation functions of charmonia by the maximum entropy method (MEM) which is a very useful and powerful tool to analyze spectral functions from lattice QCD simulations [3]. We show detailed features of charmonium spectral functions of pseudoscalar and vector channels and modification of the dispersion relation at finite momenta and discuss medium effect on them in QGP. [1] T. Matsui and H. Satz, Phys. Lett. B 178 (1986) 416, T. Hashimoto, K. Hirose, T. Kanki and O. Miyamura, Phys. Rev. Lett. 57 (1986) 2123. [2] M. Asakawa and T. Hatsuda, Phys. Rev. Lett. 92 (2004) 012001, S. Datta, F. Karsch, P. Petreczky and I. Wetzorke, Phys. Rev. D 69 (2004) 094507, H. Iida, T. Doi, N. Ishii, H. Suganuma and K. Tsumura, Phys. Rev. D 74 (2006) 074502, T. Umeda, Phys. Rev. D 75 (2007) 094502. [3] M. Asakawa, T. Hatsuda and Y. Nakahara, Prog. Part. Nucl. Phys. 46 (2001) 459. Speaker: Prof. Chiho Nonaka (Nagoya University) • 87 Quarkonium production at the LHC: QCD corrections and new observables I will discuss the impact of QCD corrections on the P_T differential cross section for quarkonium production in pp collisions at RHIC, Tevatron and LHC energies, as well as the contributions from charm-gluon fusion. I will present comparisons between the predictions of the Color Singlet Model up to alpha_s^5 with the first LHC data both for J/psi and Upsilon. I will also show predictions for the polarisation to be compared with the forthcoming LHC results. Finally, I will motivate the introduction of new observables meant to better discriminate between the different mechanisms at work in quarkonium production at the LHC. Speaker: Dr Jean-Philippe Lansberg (IPNO, Université Paris-Sud 11) • 88 J/psi production at forward rapidity in PbPb collisions at sqrt(s_NN) = 2.76 TeV, measured with the ALICE detector Heavy quarkonium states are expected to provide essential information on the properties of the high-density strongly-interacting system formed in the early stages of high-energy heavy-ion collisions. Such probes are especially promising at LHC energies, where heavy quarks are copiously produced. ALICE is the experiment at the LHC mainly dedicated to the study of nucleus-nucleus collisions. At forward rapidity (2.5 < y < 4), the production of heavy quarkonium states is measured down to pT = 0 via their mu+mu- decay channels in the Forward Muon Spectrometer. After a short description of the apparatus, the analysis of the inclusive J/psi production in the first Pb-Pb data collected in the fall 2010 at a center of mass energy of sqrt(s_NN) = 2.76 TeV will be presented. Preliminary results on the nuclear modification factor (R_AA) and the central to peripheral nuclear modification factor (R_CP) will then be discussed. Speaker: Dr Philippe Pillot (SUBATECH, Nantes) • Jets Salle de l'Europe (Imperial Palace) ### Salle de l'Europe #### Imperial Palace Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Convener: David d'Enterria (CERN) • 89 Study of jet quenching using dijets in PbPb Collisions with CMS Jets are an important tool to probe the hot, dense medium that is produced in ultra-relativistic heavy ion collisions. The large collision energy at the LHC provides copious production of dijets with energies that can be cleanly identified above the heavy ion background. The multipurpose Compact Muon Solenoid (CMS) detector is well designed to measure these hard scattering processes with its high resolution calorimeters and high precision silicon tracker. Jet quenching was observed by a significant imbalance of dijet transverse momentum in PbPb collisions at a center-of-mass energy of = 2.76 TeV. The fraction of unbalanced dijets is found to increase strongly with increasing collision centrality. The dijet imbalance persists to the highest jet momenta studied, while angular distributions are only weakly modified. The redistribution of the quenched jet energy was studied using the transverse momentum balance of charged tracks projected onto the direction of the leading jet. In contrast to pp collisions, a large fraction of the momentum balance for asymmetric jets is found to be carried by low momentum particles at large angular distance to the jet axis. Speaker: Marguerite Belt Tonjes (University of Maryland) • 90 Measurements of Jets and Jet Quenching in sqrt(s_NN)=2.76 TeV PbPb Collisions with the ATLAS Detector at the LHC Jet quenching, the parton energy loss in the hot and dense medium created in ultra-relativistic heavy ion collisions, is a well-established experimental phenomenon at RHIC. However, existing single hadron, di-hadron and multi-hadron measurements from RHIC do not provide a complete understanding of the experimental results and do not sufficiently constrain theoretical models. Reconstructed jet measurements in heavy ion collisions are expected to significantly improve experimental sensitivity to quenching and to more stringently constrain theoretical descriptions of the quark/gluon-medium interaction. Thus, prior to its commencement, it was anticipated that the LHC heavy ion program would substantially advance the study of jet quenching by providing access to jets with transverse energies in excess of 100 GeV -- sufficiently high that the underlying event would provide only a modest perturbation to the jet measurements. Immediately following turn-on of the LHC in November, 2010, that expectation was satisfied through the observation of large di-jet asymmetries that may indicate substantial jet quenching. In this talk we will present results from ATLAS measurements of single jet production, di-jet correlations and jet fragmentation in Pb+Pb collisions at$\sqrt{s_{NN} = 2.76$~TeV. These results include an update on the original di-jet asymmetry analysis using the full statistics from the Fall 2010 LHC Pb+Pb run. Speaker: Aaron Richard Angerami (Columbia University) • 91 Jet Quenching via Jet Collimation The ATLAS and CMS Collaborations recently reported strong modifications of dijet properties in heavy ion collisions. In this work, we discuss the extent to which these first data constrain the microscopic mechanism underlying jet quenching. Simple kinematic arguments lead us to identify a frequency collimation mechanism via which the medium efficiently trims away the soft components of the jet parton shower. Through this mechanism, the observed dijet asymmetry can be accomodated with values of$\hat{q}\, L$that lie in the expected order of magnitude. Speaker: Dr José Guilherme Milhano (Instituto Superior Tecnico (IST) and CERN PH-TH) • 92 Next-to-leading order analysis of inclusive jet, tagged jet and di-jet production in PbPb collisions at the LHC Jets physics is an important new area of active research at RHIC and at the LHC that paves the way for novel tests of QCD multi-parton dynamics in heavy-ion reactions. At present, perturbative QCD calculations of hard probes in “elementary” nucleon-nucleon reactions can be consistently combined with the effects of the nuclear medium up to next-to-leading order. While such accuracy is desirable for leading particle tomography, it is absolutely essential for the new jet observables. With this motivation, we present results and predictions at NLO for the recent LHC lead-lead (Pb+Pb) run at a center-of-mass energy of 2.76 TeV per nucleon-nucleon pair. Specifically, we focus on the suppression the single and double inclusive jet cross sections and demonstrate how the di-jet asymmetry, recently measured by ATLAS and CMS, can be related to these general results. The case of jets tagged by an electroweak boson is exemplified by the Z0+jet channel. We predict a signature transition from enhancement to suppression of the tagged jet reflective of the medium-induced modification of parton showers. We also present NLO results relevant to the inclusive Z0 data obtained by the CMS collaboration. Our analysis includes not only final-state inelastic parton interactions in the QGP, but also initial-state cold nuclear matter effects and non-perturbative hadronization corrections. Finally, we clarify the relation between the suppression of inclusive jets, tagged jets and di-jets and the quenching of inclusive particles on the example of the recent ALICE neutral pion attenuation data. We conclude by discussing future directions and effective theories of QCD that can help improve the accuracy of the theoretical tools for jet tomography. Speaker: Dr Ivan Vitev (Los Alamos National Laboratory) • 93 Jet Reconstruction and Jet Background Classification with the ALICE experiment in PbPb collisions at the LHC The quantification of the effect of parton energy loss, known as jet quenching, is one of the major goals of jet and high$p_T$measurements in heavy-ion collisions. Here, the aim of the reconstruction of jets, as compared to single particle measurements, is to provide a more direct access to the original parton properties and the modification of the fragmentation process in heavy-ion collisions. For a clear interpretation of the reconstructed jet properties and the measurement of the inclusive jet spectrum in heavy-ion collisions a detailed characterization of the background and its fluctuation is paramount. In particular collective effects within one event can enhance or deplete locally the level of background and modify the jet energy scale. The ALICE detector with its excellent tracking capabilities is the ideal tool to study jet reconstruction based on charged particles in the presence of correlated and uncorrelated background down to particle$p_T$of 150 MeV/$c$. We will evaluate the evolution of background effects using different probes embedded into heavy-ion data and quantify their influence on the reconstructed jet spectrum. Speaker: Dr Christian Klein-Boesing (IKP Muenster) • 94 Jet quenching from RHIC to LHC Despite a wealth of experimental data for high p_T processes in heavy-ion collisions, discriminating between different models of hard parton-medium interactions has been difficult. A large reason is that the pQCD parton spectrum at RHIC is so steeply falling that distinguishing even a moderate shift in parton energy from complete parton absorption is essentially impossible. In essence, energy loss models are effectively only probed in the vicinity of zero energy loss and as a result, only the pathlength dependence of energy loss offers some discriminating power at RHIC kinematics. At LHC, this is no longer the case: Due to the much flatter shape of the parton spectra originating from 2.76 AGeV collisions, the available data probe much deeper into the model dynamics. A simultaneous fit of the nuclear suppression both at RHIC and LHC kinematics has thus a huge potential to discriminate between various models with equally good description of RHIC data alone. Speaker: Thorsten Renk (University of Jyväskylä) • 95 Probing nuclear matter with jets and$\gamma$-hadron correlations: results from PHENIX Fully reconstructed jets and hadrons correlated with a direct photon significantly reduce energy-loss bias, the bias toward measuring particles from partons which suffer little energy loss. In d+Au collisions, one accesses the physics at large$x$, which yields important constraints for nuclear parton distribution functions. In both d+Au and A+A collisions, coherent multiple-scattering models of energy loss can be tested. In this contribution, we present the current results from the PHENIX experiment on fully reconstructed jets and direct$\gamma$-hadron correlations. Baseline measurements of jets in p+p collisions as well as their yield and correlation modifications in d+Au and Cu+Cu will be given. From$\gamma$-hadron correlations, we present the fragmentation function in p+p and Au+Au collisions and its modification in Au+Au to lower$z_T$than what has previously been studied. Implications of this data on our understanding of both cold and hot, dense nuclear matter created at RHIC are discussed. Speaker: Dr Nathan Grau (Augustana College) • QCD Phase diagram Salon Haendel AB (Imperial Palace) ### Salon Haendel AB #### Imperial Palace Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Convener: Joachim Stroth (Goethe-Universität) • 96 Moments of charge fluctuations, pseudo-critical temperatures and freeze-out in heavy ion collisions In the chiral limit and at temperatures close to the QCD phase transition temperature physical observables are expected to show universal properties that are controlled by the symmetry class of a 3-dimensional O(4) spin model [1]. Higher moments of net baryon number as well as electric charge fluctuations are sensitive to these universal features of the chiral phase transition [2]. The sixth order moments are the first moments which will diverge in the chiral limit at the QCD phase transition temperature. At non-zero values of the light quark masses the sixth order moment of baryon number fluctuations has a pronounced minimum at a pseudo-critical temperature which is close to the temperature where fluctuations of the chiral order parameter are the largest. We present a calculation of the O(4) scaling functions that control scaling properties of the net baryon number fluctuations [3]. Using these universal scaling functions as well as PNJL model calculations [4] we show that the sixth order moment of baryon number fluctuations is negative in the vicinity of the pseudo-critical temperature for the chiral transition and present new results from lattice calculations using the highly improved staggered fermion action (hisq). These QCD results are in striking contrast to hadron resonance gas model calculations. We conjecture that higher order moments of net baryon number and electric charge fluctuations are well suited to characterize freeze-out conditions in heavy ion collisions. Their experimental analysis in low-energy runs at RHIC as well as at LHC will allow to verify to what extent freeze-out occurs from a thermal medium close to criticality. [1] O. Kaczmarek et al., Phase boundary for the chiral transition in (2+1) -flavor QCD at small values of the chemical potential Phys. Rev. D83, 014504 (2011). [2] F. Karsch and K. Redlich, Probing freeze-out conditions in heavy ion collisions with moments of charge fluctuations, Phys. Lett. B695, 136 (2011). [3] J. Engels and F. Karsch, The scaling functions of the free energy density and its derivatives for the 3d O(4) model, in preparation. [4] J. Engels, B. Friman, F. Karsch, K. Redlich and V. Skokov, Fluctuations as probe of the QCD phase transition and freeze-out in heavy ion collisions at LHC and RHIC, arXiv:1103.3511. Speaker: Frithjof Karsch (Brookhaven National Laboratory) • 97 Deconfinement and chiral transition in QCD at finite temperature I will discuss new lattice results on the deconfinement and chiral aspects of the transition in QCD at nonzero temperature. I will report on calculations performed using the Highly Improved Staggered Quark (HISQ) action on Nt=6, 8 and 12 lattices. I will show the continuum extrapolation for several quantities that are discussed in connection with the transition at nonzero temperature as well as the determination of the chiral transition temperature in the continuum limit. I will also show new calculations with the asqtad action on Nt=12 lattices which, when combined with the previous Nt=8 HotQCD calculations, give a consistent result for the transition temperature in the continuum limit. Finally I will discuss new findings for the equation of state for HISQ and asqtad actions. Speaker: Dr Peter Petreczky (BNL) • 98 Transition temperature and the equation of state from lattice QCD, Wuppertal-Budapest results The QCD transition is studied on lattices up to Nt=16. The strange susceptibility the chiral condensate and the renormalized Polyakov loops are presented. The equation of state is determined on lattice with Nt-6,8,10 and at some temperature values with Nt=12. The pressure, the trace anomaly, the energy and entropy density and the speed of sound are presented as functions of the temperature in the range 100 ...1000 MeV . We give estimates for the pion mass dependence and for the contribution of the charm quark. We compare our data to the equation of state obtained by the "hotQCD" collaboration. Speaker: Zoltan Fodor (BUW) • 99 Charge fluctuations in chiral models and the QCD phase transition Fluctuations of conserved charges are key probes of the chiral phase transition in a QCD medium. Of particular phenomenological importance are studies of such fluctuations at finite baryon density. A valuable tool for assessing critical fluctuations and the thermodynamics at non-vanishing baryon density is provided by effective chiral models. We consider the Polyakov loop-extended two flavors chiral quark--meson model (PQM) and discuss critical phenomena related with the spontaneous breaking of chiral symmetry. The model is explored beyond the mean-field approximation in the functional renormalisation group (FRG) approach. We formulate and solve the renormalization group flow equation for the scale-dependent thermodynamic potential in the presence of the gluonic background field at finite temperature and density [1] and determine the phase diagram of the PQM model in the FRG approach [2]. We also consider properties of the net-quark number density fluctuations as well as their higher cumulants [3] and discuss the influence of nonperturbative effects on their properties near the chiral crossover transition. With increasing net-quark number density, the higher order cumulants show a strong dependence on the chiral crossover transition. This is illustrated by exploring the ratios of moments of net-baryon number and electric charge fluctuations. We discuss their role as probes of deconfinement and the chiral phase transition in heavy ion collisions at RHIC and LHC. [1] V. Skokov, B. Stokic, B. Friman, K. Redlich, Phys.Rev.C82:015206,2010. [2] V. Skokov, B. Friman, K. Redlich, arXiv:1008.4570 [3] B. Friman, F. Karsch, K. Redlich, V. Skokov, arXiv:1103.3511 Speaker: Dr Vladimir Skokov (GSI, Darmstadt, Germany) • 100 Lattice QCD based equation of state at finite baryon density The effects of non-zero baryon density are expected to become important in hydrodynamic modeling of heavy collisions below the highest energy at RHIC. Recent calculations in effective models and in QCD using Dyson Schwinger equation suggest that the transition in QCD remains a crossover up to baryon chemical potentials of about 800MeV [1]. If so, the equation of state relevant for hydrodynamic models can be calculated on the lattice using Taylor expansion. However, there are large cutoff effects in present lattice calculations for non-zero chemical potentials. We employ the lattice QCD data on Taylor expansion coefficients [2] to extend our previous parametrization of the equation of state [3] to finite baryon density. When we take into account lattice spacing and quark mass dependence of the hadron masses [3], the Taylor coefficients at low temperature are equal to those of hadron resonance gas. Therefore we require require that the equation of state is smoothly connected to the hadron resonance gas equation of state at low temperatures. Some preliminary results were reported in [4]. We also show how the hydrodynamical evolution is affected by this equation of state in the energy range relevant for SPS and the RHIC energy scan. [1] T.K. Herbst et al, Phys. Lett. B696 (2011); C.S. Fischer et al, arXiv:1104.1564 [2] M. Cheng et al, Phys. Rev. D79 (2009) 074505; C Miao and C. Schmidt,PoS LATTICE2008 (2008) 172 [3] P.Huovinen and P.Petreczky, Nucl.Phys. A837 (2010) 26 [4] P.Huovinen and P.Petreczky, J. Phys. Conf. Ser. 230 (2010) 012012 Speaker: Dr Pasi Huovinen (Johann Wolfgang Goethe-Universität) • 101 Scale for the phase diagram of quantum chromodynamics We present a test of QCD in the non-perturbative domain through a comparison of thermodynamic fluctuations predicted in lattice computations with the experimental data of baryon distributions in high-energy heavy-ion collisions. This study provides evidence for thermalization in these collisions, and allow us to set a scale for the QCD phase diagram. The scale is the temperature for the cross over from normal nuclear matter to the deconfined quark gluon plasma phase. Extension of these techniques might allow the identification of the critical point of QCD. Speaker: Prof. Sourendu Gupta (TIFR, Mumbai) • 102 QCD thermodynamics at intermediate coupling The weak-coupling expansion of the QCD free energy is known to order g^6*log[g], however, the resulting series is poorly convergent at phenomenologically relevant temperatures. I will discuss how the gauge invariant hard-thermal-loop perturbation theory (HTLpt) reorganization of the calculation improves the convergence of the successive approximations to the QCD free energy. I will present new results of an HTLpt calculation of QCD thermodynamics to three loops. The results of this calculation are consistent with lattice data down to 2-3T_c. This is a non-trivial result since, in this temperature regime, the QCD coupling constant is neither infinitesimally weak nor infinitely strong with g~2, or equivalently alpha_s~0.3. Therefore, we have a crucial test of the quasiparticle picture in the intermediate coupling regime. Our results suggest that HTLpt provides a systematic framework that can be used to calculate static and dynamic quantities for temperatures relevant at LHC. Speaker: Dr Nan Su (Bielefeld University) • Poster Session 1 + Wine and Cheese Tente Imperiale, Salons Berlioz AB/Verdi AB (700) ### Tente Imperiale, Salons Berlioz AB/Verdi AB (700) #### Centre Bonlieu France Poster Session 1 + Wine and cheese • Wednesday, May 25 • Hard probes I: hadron spectra Théâtre National ### Théâtre National #### Centre Bonlieu 1 Rue Jean Jaurès, 74000 Annecy, France Tel : + 33 04 50 45 00 33 Convener: Miklos Gyulassy (Columbia University) • 103 Particle production at large transverse momentum with ALICE We present transverse momentum distributions of charged particles and identified hadrons in pp and Pb-Pb collisions, measured by ALICE at the LHC. The Pb-Pb data are presented in intervals of the collision centrality and cover transverse momenta up to 50 GeV/c. Nuclear medium effects are studied in terms of the nuclear modification factor R_AA. The results indicate strong suppression of high-p_T particles in Pb-Pb collisions, consistent with a large energy loss of hard-scattered partons in the hot, dense, and long-lived medium created at the LHC. Speaker: Harald Appelshaeuser (Johann-Wolfgang-Goethe Univ.) • 104 Nuclear modification factors from the CMS experiment We report the measurement of transverse momentum spectra of the charged hadrons and photons in √sNN = 2.76 TeV PbPb collisions with the CMS detector. The nuclear modification factors are constructed by dividing the PbPb pT spectra, normalized to the number of binary collisions, by the pp references. Speaker: Yen-Jie Lee (Massachusetts Inst. of Technology (MIT)) • 105 Recent R_{AA} Results from the PHENIX Experiment Speaker: Dr Martin Purschke (BROOKHAVEN NATIONAL LABORATORY) • 106 Quenching of single hadron and photon spectra from RHIC to LHC I will discuss the generic features of parton energy loss effects on the quenching of large-pT hadrons, as well as more quantitative studies. The differences expected from RHIC to LHC will be highlighted. The quenching of prompt photons will also be discussed in detail. Finally, I will stress the need for precise baseline measurements of hadrons and photons in pp and pPb collisions. Speaker: Francois Arleo (lapp-Laboratoire d'Annecy-le-Vieux de Physique des Particules-In) • 107 Common discussion with 4 speakers Speaker: Miklos Gyulassy (Columbia University) • 10:20 AM Coffee break Théâtre National ### Théâtre National #### Centre Bonlieu France • Hard probes II: true jets Théâtre National ### Théâtre National #### Centre Bonlieu 1 Rue Jean Jaurès, 74000 Annecy, France Tel: +33 4 50 45 00 33 Convener: Peter Jacobs (Lawrence Berkeley National Laboratory) • 108 Monte Carlo tools for jet quenching Speaker: Korinna Zapp (University of Heidelberg) • 109 STAR on reconstructed jets and jet-like correlations Speaker: Helen Louise Caines (Yale University-Unknown-Unknown) • 110 Jet measurements by the CMS experiment in pp and PbPb collisions The energy loss of fast partons traversing the strongly interacting matter produced in high-energy nuclear collisions is one of the most interesting observables to probe the nature of the produced medium. The multipurpose Compact Muon Solenoid (CMS) detector is well designed to measure these hard scattering processes with its high resolution calorimeters and high precision silicon tracker. Analyzing data from pp and PbPb collisions at a center-of-mass energy of 2.76 TeV parton energy loss is observed as a significant imbalance of dijet transverse momentum. To gain further understanding of the parton energy loss mechanism the redistribution of the quenched jet energy was studied using the transverse momentum balance of charged tracks projected onto the direction of the leading jet. In contrast to pp collisions, a large fraction the momentum balance for asymmetric jets is found to be carried by low momentum particles at large angular distance to the jet axis. Further the fragmentation functions for leading and subleading jets were reconstructed and are compared to model calculations and measurements in pp collisions. The results confirm and complement earlier CMS results based on calorimeter jets and yield a detailed picture of parton propagation in the hot QCD medium. Speaker: Dr Christof Roland (Massachusetts Institute of Technology) • 111 ATLAS jet measurements Speaker: Brian Cole (Physics Dept., Pupin Physics Lab.-Columbia University-Unknown) • 112 Common discussion with 4 speakers Speaker: Peter Jacobs (Lawrence Berkeley National Laboratory) • 12:45 PM Lunch break Restaurant la Voile, Brasserie du Parc/Rotonde du Parc (Imperial Palace) ### Restaurant la Voile, Brasserie du Parc/Rotonde du Parc #### Imperial Palace La Voile 200P brasserie 500P • Excursion 1 • IAC Salon Ravel B (Imperial Palace) ### Salon Ravel B #### Imperial Palace • 113 QM2011 Speaker: Yves Schutz (IN2P3/CERN) • 114 Preparation of QM2012 at Washington Speakers: Dima Kharzeev (Unknown), John Harris (Yale), Thomas Ullrich (Brookhaven National Laboratory) • 115 Proposal for QM13/14 in Japan Speakers: Prof. Hideki Hamagaki (Graduate School of Science-University of Tokyo), Kenta Shigaki (Hiroshima University) • 116 Proposal for QM13/14 in Darmstadt Speaker: Peter Braun-Munzinger (Gesellschaft fuer Schwerionenforschung mbH (GSI)) • 117 Proposal for QM13/14 in Bologna Speaker: Luisa Cifarelli-Strolin (Dipartimento di Fisica) • 118 Proposal for a QM in Brazil Speaker: Kodama Takeshi • Thursday, May 26 • Correlations & fluctuations: I Théâtre National ### Théâtre National #### Centre Bonlieu Convener: Prof. Krzysztof Redlich (University of Wroclaw, Institute of Theoretical Physics) • 119 Correlations and fluctuations from lattice QCD Speaker: Swagato Mukherjee (Brookhaven National Laboratory) • 120 STAR: results from the beam energy scan program Speaker: Bedangadas Mohanty (Variable Energy Cyclotron Centre, Kolkata) • 121 NA49/NA61: SPS results on fluctuations & correlations Speaker: Marek Gazdzicki (Frankfurt University) • 122 Production of identified particles in pp and PbPb collisions at LHC energies with the ALICE detector The ALICE experiment is taking data since 2009, with proton and lead beams. In this talk, we review the different particle identification techniques used by the experiment and the excellent performance during the first year of data taking. We summarize the current results on identified particle spectra in pp collisions at sqrt(s) = 900 GeV and 7 TeV, and in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. In particular, the energy dependence of the spectral shapes of the pp data is discussed and the results are compared to previous experiments and commonly used Monte Carlo models. The evolution of the particle spectra in PbPb with collision centrality is presented. Various particle ratios are shown, including the baryon/meson ratio (Lambda/K0s). Finally, we conclude with an overview of the ongoing analyzes on identified particles. Speaker: Michele Floris (CERN) • 123 Common discussion with 4 speakers Speaker: Prof. Krzysztof Redlich (University of Wroclaw, Institute of Theoretical Physics) • 10:20 AM Coffee break Centre Bonlieu ### Centre Bonlieu #### Centre Bonlieu 1 Rue Jean Jaurès, 74000 Annecy, France Tel : + 33 04 50 45 00 33 • Correlations & fluctuations: II Théâtre National ### Théâtre National #### Centre Bonlieu France Convener: Volker Koch (LBNL) • 124 Fluctuations & correlations – TH perspective Speaker: Matthew Luzum (IPhT CEA/Saclay) • 125 Correlations and fluctuations measured by the CMS experiment in pp and PbPb collisions Measurements of charged dihadron angular correlations are presented in proton-proton (pp) and Lean-Lead (PbPb) collisions, over a broad range of pseudorapidity and azimuthal angle, using the CMS detector at the LHC. In very high multiplicity pp events at center-of-mass energy of 7 TeV, a striking "ridge"-like structure emerges in the two-dimensional correlation function for particle pairs with intermediate pT of 1-3 GeV/c, in the kinematic region 2.0 < |Delta eta| < 4.8 and small Delta Phi, which is similar to the observation in heavy-ion collisions. Updated studies of this new effect as a function of particle transverse momentum, rapidity and event characteristics are shown and discussed in comparison to various model calculations. The long-range and short-range dihadron correlations are also studied in PbPb collision at a nucleon-nucleon center-of-mass energy of 2.76 TeV. The dependence of the jet-and ridge-region shape and yield on transverse momentum and collision centrality has been measured. A Fourier analysis of the long-range dihadron correlations will be presented and discussed in the context of CMS measurements of higher order flow coefficients. Speaker: Wei Li (MIT) • 126 Results from correlation studies in ALICE The talk presents results from hadron correlations in PbPb collisions at 2.76 TeV with ALICE. Untriggered di-hadron correlations studies are shown which provide a map of the bulk correlation structures in heavy-ion collisions. The long-range correlation region is further studied by triggered correlations which addresses the dependence on trigger and associated pT. The measured correlation functions are decomposed with a multi-parameter fit and into Fourier components. The jet yield modification factor I_AA extracted using triggered correlations is presented. Speaker: Jan Fiete Grosse-Oetringhaus (CERN) • 127 STAR correlations and fluctuations Speaker: Paul Sorensen (BNL) • 128 Common discussion with 4 speakers Speaker: Volker Koch (Lawrence Berkeley National Laboratory) • 12:45 PM Lunch break Restaurant la Voile, Brasserie du Parc/Rotonde du Parc (Imperial Palace) ### Restaurant la Voile, Brasserie du Parc/Rotonde du Parc #### Imperial Palace • Electromagnetic probes Salon Ravel AB (Imperial Palace) ### Salon Ravel AB #### Imperial Palace Convener: Toru Sugitate (Hiroshima University) • 129 Weak boson production measured in PbPb and pp by CMS The unprecedented centre-of-mass energy available at the LHC offers unique opportunities for studying the properties of the strongly-interacting QCD matter created in PbPb collisions at extreme temperatures and very low parton momentum fractions. With its high precision, large acceptance for tracking and calorimetry, and a trigger scheme that allows the analysis of almost each minimum bias PbPb event by the high-level trigger, CMS is fully equipped to measure muons and electrons in the high multiplicity environment of nucleus-nucleus collisions. Electroweak boson production is an important benchmark process at hadron colliders. Precise measurements of Z production in heavy-ion collisions can help to constrain nuclear PDFs as well as serve as a standard candle of the initial state in PbPb collisions at the LHC energies. The inclusive and differential measurements of the Z boson yield in the muon decay channel will be presented, establishing that no modification is observed with respect to next-to-leading order pQCD calculations, scaled by the number of incoherent nucleon-nucleon collisions. The status of the Z measurement in the electron decay channel, as well as the first observation of W→μν in heavy ion collisions will be given. The heavy-ion results will be presented in the context of those obtained in pp collisions with the CMS detector. Speaker: Jorge A Robles (University of California (UCD)) • 130 Leptonic observables in sqrt(s_NN)=2.76 TeV PbPb collisions measured with the ATLAS detector at the LHC A broad program of measurements using heavy ion collisions is underway in ATLAS, with the aim of studying the properties of QCD matter at high temperatures and densities. Leptonic observables are essential tools for the study of heavy ion collisions since leptons do not interact strongly and thus pass through the strongly-coupled medium unaffected. The centrality dependence of J/psi and Z yields, observed through their di-muon channel, are important measurements both for assessing modifications of particle production as well as probing particular regions of the nuclear PDFs. W boson measurements are also possible using single leptons, and provide another handle on the initial state. This talk describes measurements performed using up to 9 µb-1 of lead-lead collision data provided at a nucleon-nucleon center-of-mass energy of 2.76 GeV by the Large Hadron Collider and collected by the ATLAS Detector during November and December 2010 Speaker: Dr Rikard Sandström (Max Planck Institut) • 131 Dielectron Continuum Production from$\sqrt{s_{NN}}$= 200 GeV pp and Au+Au collisions at STAR Dilepton distributions have been proposed as one of the penetrating probes for hot and dense nuclear matter created in high-energy nuclear collisions. Due to their relatively small final-state interaction cross-sections with the hot/dense environment, dileptons bring us direct information of the created matter in such collision. Since dileptons are created over all stages of heavy ion reactions, their sources vary as a function of kinematics. In the low mass region (LMR: mass<1.1GeV/$c^{2}$), dileptons are dominated by vector mesons and directed photons, while in the intermediate mass region (IMR: 1.1< mass< 3GeV/$c^{2}$) dileptons are dominated by thermal radiation of quark gluon plasma (QGP). In the high mass region (HMR: mass> 3 GeV/$c^{2}$), dileptons are mostly contributed by heavy (charm and bottom) quark decays and Drell-Yan processes. As a result, the dilepton distributions, especially in the IMR and HMR, could provide new aspects of early collision dynamics in heavy ion collisions. With the completion of the full barrel time-of-flight detector, the electron identification has been significantly improved at STAR, especially in low momentum region. In this talk we will present the first STAR results on dielectron production in p+p and Au+Au collisions at$\sqrt{s_{NN}}$= 200 GeV. The results will be compared to hadron decay cocktails to search for vector meson in-medium modifications in LMR and the QGP thermal radiation in IMR. A systematic analysis of the transverse mass distributions in IMR region as a function of the mass in Au+Au collisions will be discussed. The results will be compared to those from 200 GeV p+p collisions as well as the results from SPS energies. Speaker: Jie Zhao (SINAP/LBNL) • 132 Measurements of low mass dielectrons in Au+Au collisions with the HBD upgrade of the PHENIX detector Dileptons are valuable probes in the investigation of the hot and dense matter formed in heavy ion collisions, since they interact only electromagnetically and thus their path from the interaction region to the detectors is almost undisturbed. They can provide information about the matter properties in the early stages of the collisions where deconfinement and chiral symmetry restoration are expected to take place. However, the measurements of dileptons in heavy ion collisions are challenging due to the overwhelming yield of pi0 Dalitz decays and photon conversions, which produce a large combinatorial background especially in the low invariant mass region (m_ee<1 GeV/c^2). The PHENIX spectrometer has been upgraded with a Hadron Blind Detector (HBD) with the purpose of reducing the combinatorial background from the dielectron mass spectrum. The HBD is a windowless Cherenkov detector, operating with pure CF_4, using triple GEM elements with a CsI photocathode and pad readout. The HBD reduces the combinatorial background by exploiting the small opening angle of the pi0 Dalitz and conversion pairs. It was successfully operated during Run 9 and Run 10 at RHIC in the measurements of e+e- pairs in p+p collisions at sqrt(s)=200 GeV and in Au+Au collisions at sqrt(s_NN) = 200 GeV, 62 GeV and 39 GeV. In this talk a full account of the HBD and present results of the dielectron analysis in Au+Au collisions at sqrt(s_NN)=200 GeV with improved signal to background ratio, will be presented. Speaker: Mihael Makek (Weizmann Institute of Science) • 133 Enhancement of thermal photon production in event-by-event hydrodynamics Thermal photon emission is widely believed to reflect properties of the earliest, hottest evolution stage of the medium created in ultra-relativistic heavy-ion collisions. Previous computations of photon emission have been carried out using a hydrodynamical medium description with smooth, averaged initial conditions. Recently, more sophisticated hydrodynamical models which calculate observables by averaging over many evolutions with event-by-event fluctuating initial conditions (IC) have been developed. Given their direct connection to the early time dynamics, thermal photon emission appears an ideal observable to probe fluctuations in the medium initial state. In this work, we demonstrate that including fluctuations in the IC may lead to an enhancement of the thermal photon yield of about a factor of 2 in the region$2 < p_T < 4$GeV/$c$(where thermal photon production dominates the direct photon yield) compared to a scenario using smooth, averaged IC. Consequently, a better agreement with PHENIX data is found. This can be understood in terms of the strong temperature dependence of thermal photon production, translating into a sensitivity to the presence of 'hotspots' in an event and thus establishing thermal photons as a suitable probe to characterize IC fluctuations. Ref:arXiv:1102.4706[Hep-ph]. Speaker: Rupa Chatterjee (University of Jyvaskyla) • 134 Direct photon production in heavy ion collisions in PHENIX experiment at RHIC E.Kistenev for the PHENIX Collaboration Direct photon production in heavy ion collisions in PHENIX experiment at RHIC Among the observables used to probe the high temperature and high density phase of heavy nucleus collisions direct photons are considered of particular interest. At LO direct photons are produced in quark-gluon Compton scattering and quark-antiquark annihilation, the NLO processes are dominating in bremsstrahlung and fragmentation photon production and jet re-interaction in medium, QGP and hot hadronic stage emit thermal photons. Correlated measurements of the transverse momentum dependence of direct photon production in collisions of different species and of underlying event observables, like isolation or flow, as well as the nuclear modification factor may give insight into the relative contribution from various production mechanisms. Extracting the direct photon signal from the large hadron decay background is experimentally challenging particularly at lower transverse momenta and high multiplicities. PHENIX used a combination of techniques based upon virtual (via low to intermediate mass e+e- pairs) and real (neutral clusters in calorimeters and reconstructed e+e- pairs from photon conversions) photon measurements to determine direct photon yields in the range of transverse momenta up to about 20 GeV/c for a wide range of energies and colliding species. In this talk we present recent PHENIX results on total direct photon production in pp, dA and AA collisions with emphasis on azimuthal correlations and nuclear modification. Implications of the PHENIX measurements for the initial temperature and density estimates as well as for the space-time evolution of the fireball will also be discussed. Speaker: Dr Edouard Kistenev (Brookhaven National Laboratory) • 135 Photons at RHIC and at the LHC: the role of viscosity and of event-by-event fluctuations We investigate the yield and the azimuthal anisotropy of produced photons in heavy-ion collisions at RHIC and at LHC energies. We study the photons produced from a variety of sources, including those from primordial nucleon-nucleon collisions, from thermal partons, from fragmenting QCD jets, from jets interacting with thermal partons, and from thermal hadrons. We study the interplay of those sources, in an evolving 3D simulation of the colliding system that involves hydrodynamics and hard jets. We study ideal and viscous fluids, and we evaluate the effect of fluctuating initial conditions, and of using different hadronic equations of state. Under all of the above conditions, we quantify the ability of real photons to act as penetrating probes of the hot and dense strongly interacting medium. Speaker: Prof. Charles Gale (McGill University) • Future facilities and experiment upgrades Salon Haendel AB (Imperial Palace) ### Salon Haendel AB #### Imperial Palace Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Convener: Daicui Zhou (Institute of Particle Physics-Hua-Zhong Normal University) • 136 Probing the gluonic structure of matter at a future Electron-Ion Collider The probing of nuclei and nucleons via deep-inelastic and diffractive processes in the high-energy (low-x) regime will open a new precision window for the investigation of the gluonic structure of matter. Studies of e+p collisions at HERA and especially d+Au collisions at RHIC have found tantalizing hints of saturated gluon densities, a phenomenon with substantial impact on the physics of heavy-ion collisions. Unveiling the collective behavior of densely packed gluons under conditions where their self-interactions dominate will require an Electron-Ion Collider (EIC): a new facility with capabilities well beyond those of any existing accelerator. Such a collider could be sited either at BNL or JLAB. In my talk I will outline the compelling physics case for e+A collisions with a focus on the opportunities for small-x physics. I will discuss the related key measurements and give a brief status of machine concepts, detector design, and timeline. Speaker: Thomas Ullrich (Brookhaven National Laboratory) • 137 eA collisions at the Large Hadron-electron Collider I will show the possibilities for electron-ion studies offered by the proposed electron-hadron collider at CERN, the Large Hadron-electron Collider [1]. After a short introduction on open problems at small x, I will briefly present the machine and detector. Then I will focus on small-x aspects in electron-nucleus collisions, first on inclusive measurements and the determination of nuclear parton densities, and then on diffraction. I will finish by discussing some opportunities for final state studies. [1] M. Klein et al., Prospects for a Large Hadron Electron Collider (LHeC) at the LHC, EPAC'08, 11th European Parti cle Accelerator Conference, 23- 27 June 2008, Genoa, Italy; http://cern.ch/lhec. Speaker: Nestor Armesto Perez (Universidade de Santiago de Compostela) • 138 Heavy ion program at JINR NICA/MPD facility New project NICA/MPD (Nuclotron-based Ion Collider fAcility/MultiPurpose Detector) is now under realization phase at JINR (Dubna). The main goal of the project is to start in the coming years an experimental study of hot and dense strongly interacting matter and search for possible signs of the mixed phase and critical endpoint in heavy ion collisions. This study should be carried out at centre-of-mass ion collision energies of √sNN = 4-11 GeV (NN-equivalent) and at average luminosity of 10E27 cm-2 s-1 for Au (79+). The program also foresees start-up of fixed target experiments with the extracted beams from upgraded JINR synchrotron Nuclotron at energies up to 5.81 GeV/u (scaled to A/Z = 2) and intensity up to 5*10E8 s-1 (for Au 79+). Another goal of the project is aimed to study the spin structure of nucleon and the other spin sensitive phenomena with colliding beams of polarized protons and deuterons. The SPD (Spin Physics Detector) setup aimed at that purpose is under design. Speaker: Prof. Alexander Sorin (Joint Institute for Nuclear Research) • 139 ALICE detector upgrades The ALICE experiment is specifically designed for the study of strongly interacting matter as created in heavy ion collisions at LHC. With some of its particular features, like the very good measurement of low momentum particles and the particle identification capabilities it also provides unique measurements in p+p collisions. However, very recent developments in heavy ion physics suggest that some more enhanced measurement capabilities will be strongly desirable to obtain a deeper understanding of the new matter created. ALICE is setting up a program of detector upgrades, which could to a large extent be installed in the long LHC shutdown foreseen for 2017/18, to address these new scientific challenges. Projects considered include an upgrade of the inner tracking system (ITS), the installation of a new forward calorimeter (FOCAL), the extension of the muon spectrometer (MFT, muon forward tracker), the installation of a detector with enhanced particle identification at high momentum (VHMPID), and additional detectors enhancing the capabilities for diffractive physics (AD = ALICE Diffractive). An increased rate capability of the largest detector in ALICE, the time projection chamber (TPC), is also under investigation, and it is foreseen to improve the data acquisition and high level trigger systems (DAQ & HLT) to achieve more bandwidth and to use more sophisticated and complex triggers. We will discuss the scientific frontiers and will present the corresponding upgrade projects under study for the ALICE experiment. Speaker: Prof. Thomas Peitzmann (Universiteit Utrecht) • 140 The next decade of physics with PHENIX The first decade of RHIC physics and the first heavy ion running at the LHC have produced a wealth of data and discoveries. It is timely to now evaluate what has been learned and ask what compelling new questions have been raised. In this talk, several key unanswered questions about the properties of the strongly coupled quark gluon plasma and the distribution of partons inside nucleons and nuclei will be discussed along with how they can be addressed experimentally. The PHENIX Collaboration has developed a plan for upgrading the experiment in order to address these new questions. The current status of these plans will be presented. Speaker: Anne Sickles (Brookhaven) • 141 STAR science for the coming decade The STAR Collaboration has identified eight key questions that will drive RHIC science during the coming decade, six of which involve ultrarelativistic heavy-ion collisions. What is the nature of the initial state in nuclear collisions? What are the properties of the strongly-coupled system produced at RHIC, and how does it thermalize? Are the interactions of energetic partons with QCD matter characterized by weak or strong coupling, and what is the detailed mechanism for partonic energy loss? Where is the QCD critical point and the associated first-order phase transition line? Can we strengthen current evidence for novel symmetries in QCD matter and open new avenues? What exotic particles are created at RHIC? The STAR detector, with its large acceptance tracking, calorimetry, and particle identification, is an ideal tool to explore these questions. Complete answers nonetheless will require detector upgrades. Near-term upgrades, including the Heavy Flavor Tracker and Muon Telescope Detector, will enable a rich program of heavy flavor physics. Upgrades to the forward region will enable detailed studies of the partonic structure of nuclei and the onset of gluon saturation. An additional suite of upgrades during the latter part of the decade will position STAR to make crucial measurements in e+p and e+A collisions during the early phase of eRHIC. The talk will provide an overview of this STAR decadal plan. Speaker: Prof. Carl Gagliardi (STAR Collaboration) • 142 Cross section normalization in ALICE Measurements of reference trigger cross sections were obtained with the ALICE detector, based on beam properties measured from van der Meer scans where convolution of the beam profiles were evaluated. The measurement is essential for absolute cross section determination of the physics processes. Based on this measurement, inelastic cross sections characterizing proton-proton collisions at LHC energies were obtained with the ALICE detector with a detailed detector Monte-Carlo simulations. As second example, cross sections of reference process, with at least one charged particle is produced in pseudorapidity range of$-0.8<\eta<0.8$, was measured. These results obtained for$\sqrt{s}$=2.76 TeV and 7 TeV are compared to measurements from other experiments as well as to recent calculations based on Regge theories for inelastic cross sections. The detail descriptions of thees measurements and analysis methods will be presented. The presentation will focuses also on instrumental and technical aspects of detectors and accelerators. Speaker: Dr Ken Oyama (University of Heidelberg) • Jets Salle de l'Europe ### Salle de l'Europe #### Centre Bonlieu France Convener: Mateusz Ploskon (Lawrence Berkeley National Laboratory) • 143 Charged particle production at large transverse momentum in PbPb collisions at sqrt(s)=2.76 TeV measured with ALICE at the LHC. The observed suppression of high-pT particle production in heavy-ion collisions is generally attributed to energy loss of partons as they propagate through the hot and dense QCD medium. Inclusive transverse momentum spectra of primary charged particles in Pb-Pb collisions at sqrt(s)=2.76 TeV have been measured by the ALICE Collaboration at the LHC. The data are presented in intervals of collision centrality. The charged particle spectra are compared to those measured in pp collisions at the same collision energy, scaled by the number of underlying nucleon-nucleon collisions. This comparison is expressed in terms of the nuclear modification factor R_AA. The results indicate only weak medium effects in peripheral collisions, while there is clear evidence for strong medium effects in central collisions. In this talk we will present the results of an analysis of the full Pb-Pb statistics obtained in the Nov. 2010 run. With these data the transverse momentum range covered is increased to 50 GeV/c as compared to previous studies of R_AA by ALICE. The evolution of R_AA with collision centrality and transverse momentum will be discussed. Speaker: Jacek Otwinowski (Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany) • 144 Measurements of charged particle spectra in sqrt(s_NN)=2.76 PbPb collisions with the ATLAS detector at the LHC The measurement of charged particle spectra in heavy ion collisions is a direct way to study properties of hot and dense matter created in these interactions. The centrality dependence of the spectral shape is an important tool to understand the interplay between collective flow and energy loss mechanisms. The ATLAS detector at the LHC took lead-lead data at 2.76 TeV per nucleon-nucleon pair with an integrated luminosity of just over 9µb-1. The ATLAS inner detector consists of 3 layers of silicon pixel detectors and 4 double sided strip layers in the barrel regions, with pixel and strip discs covering the forward region out to$|\eta|=2.5$. Due to the excellent capabilities of the ATLAS detector, and its stable operation during the first heavy ion run, these data allow measurements of the charged particle spectra and their ratios in different centrality bins over a wide range of transverse momenta and pseudorapidity. Comparison of ATLAS results to the results measured at lower energy will provide the opportunity to study the differences between the medium formed at the LHC and RHIC. Speaker: Alexander Milov (Weizmann Institute of Science) • 145 Pion quenching and tomography from RHIC to LHC in the WHDG model We present parameter-free predictions from the WHDG (radiative+elastic+geometric fluctuation) energy loss model for high pT pion suppression in A+A at 2.76 and 5.5 ATeV. The input density is constrained from a rigorous statistical analysis of RHIC pi0 quenching data. The predictions are consistent with the recent _charged_ hadron RAA data from ALICE only within the current very large systematic uncertainty (due to the unmeasured reference p + p spectrum). However, our constrained prediction of central to peripheral pion R_cp(pT), in which reference p + p spectra uncertainties cancel, is found to be over-quenched by ~two sigma relative to the charged hadron ALICE R_cp data at all pT<20 GeV. The basic tomographic assumptions in WHDG are (1) the energy loss scales linearly with the initial QGP density, rho0, and (2) that rho0 scales linearly with charge particle multiplicity dNch/dy. Under these assumptions, WHDG predicts significant difference in magnitude and pt slope pf pion RAA between RHIC and LHC. Future ALICE identified pi,K,p hadron RAA data (as well as accurate p + p and p + Pb reference data) will enable more quantitative jet tomographic tests of hard probe dynamics in strongly interacting quark gluon plasmas. Speaker: William Horowitz (University of Cape Town) • 146 Suppression of high p_T hadrons in PbPb Collisions at LHC Nuclear modification factor$R_{AA}(p_{T})$for large transverse momentum pion spectra in$Pb+Pb$collisions at$\sqrt{s}=2.76$TeV is predicted within the NLO perturbative QCD parton model. Effect of jet quenching is incorporated through medium modified fragmentation functions within the higher-twist approach. The jet transport parameter that controls medium modification is proportional to the initial parton density and the coefficient is fixed by the RHIC data on suppression of large$p_{T}$hadron spectra. Data on charged hadron multiplicity$dN_{ch}/d\eta=1584 \pm 80$in central$Pb+Pb$collisions from the ALICE Experiment at the LHC are used to constrain the initial parton density both for determining the jet transport parameter and the 3+1D ideal hydrodynamic evolution of the bulk matter that is employed for the calculation of$R_{PbPb}(p_{T})$for neutral pions Speaker: Prof. Hanzhong Zhang (IOPP) • 147 Centrality and transverse momentum dependence of the nuclear modification of charged particle spectra in PbPb collisions at 2.76 TeV from CMS The nuclear modification factor R_AA is one of the key signatures for the energy loss of fast partons traversing a QCD medium. Charged particle transverse momentum (pT) spectra have been measured by CMS for pp collisions at sqrt(s)=0.9 and 7 TeV, corresponding to integrated luminosities of 231 ub-1 and 2.96 pb-1, respectively. Calorimeter-based high-transverse-energy jet triggers are employed to enhance the statistical reach of the high-pT measurements. The results are compared to various generator tunes and also to an empirical scaling of different collision energies with xT=2pT/sqrt(s) over the pT range up to 200 GeV/c. Using a combination of xT scaling and direct interpolation at fixed pT, a reference pT spectrum at sqrt(s)=2.76 TeV is constructed from pT = 1-100 GeV/c with less than 13% systematic uncertainty. We have obtained R_AA in bins of collision centrality for a PbPb data sample with an integrated luminosity of 7 ub-1, dividing by the interpolated reference spectrum. As seen at lower energies, the charged particle spectrum in central PbPb collisions is suppressed by at least a factor of five (R_AA < 0.2) compared to binary scaling around pT = 5-10 GeV/c. Above pT = 10 GeV/c, however, there is a significant rise in the nuclear modification factor, which will be presented out to pT = 80 GeV/c. Speaker: Andre Yoon (Massachusetts Inst. of Technology (MIT)) • 148 Suppression of neutral pion production at large transverse momentum measured with the ALICE experiment in PbPb collisions at$\sqrt{s_{NN}}$=2.76 TeV The ALICE experiment at the LHC has measured the transverse momentum spectra of neutral mesons via the two photon decay in pp and Pb-Pb collisions at$\sqrt{s_{NN}}$=2.76 TeV over a wide transverse momentum range with different subsystems: with the electromagnetic calorimeters PHOS and EMCAL and via conversions of the photons in the inner material of the experiment to e+e--pairs reconstructed with the Central Tracking System. In this talk, the production of neutral pions in pp and Pb-Pb collisions is compared in terms of the so called nuclear modification factor,$R_{AA}$, for different centrality selections of the Pb-Pb data sample. Speaker: Dr Gustavo Conesa Balbastre (LPSC - Grenoble) • 149 Medium-induced modifications of color flow in high transverse momentum processes Heavy ion collisions at both RHIC and the LHC show strong medium-induced modifications of high-pT single inclusive hadron spectra, jet-like particle correlations and reconstructed jets. A dynamical understanding of these jet quenching phenomena is typically sought within a partonic picture in which the energy of highly energetic parent partons is degraded due to multiple inelastic and/or elastic interactions inside QCD matter. In the current model implementations of this parton energy loss the hadronization process is unaffected by it on account that for sufficiently energetic projectiles time dilation should guarantee their hadronization outside the medium. However, as it has been pointed out before, the interaction of a colored parton with a QCD medium modifies the color flow of the parton shower and arguably can imprint on the hadronization process at much higher transverse momentum than estimated previously. In this context, we present here the first QCD-based calculation of medium-induced color flow. Decomposing the multiple scattering diagrams of the BDMPS-Z formalism for parton energy loss into color-singlet 'prehadronic' systems, we observe that (in comparison to vacuum fragmentation) medium-induced effects do not only degrade the longitudinal momentum of these color-singlet systems but also strongly enhance their invariant mass. The larger the invariant mass of a color-singlet at the end of the perturbative evolution, the more likely it is for such system to decay into a larger number of hadronic fragments and thus leave a smaller fraction of the total available energy to the leading hadron. Therefore, for multi-partonic states that show the same kinematic distributions at the end of the perturbative evolution, medium-modified color flow can be a significant additional source of medium-induced multiplicity increase and medium-induced degradation of the leading hadron. We illustrate this general observation in simple models. We also identify a color flow specific formation time argument that indicates that effects of color-flow induced additional suppression can persist over transverse energies up to tens of GeV, and may contribute to an enhanced slope of the nuclear modification factor. Speaker: Dr Andrea Beraudo (Centro Studi e ricerche "Enrico Fermi" - Rome (Italy)) • Pre-equilibrium and initial state Rotonde de l'Europe (150) (Imperial Palace) ### Rotonde de l'Europe (150) #### Imperial Palace Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Convener: Carlos Pajares (Unknown) • 150 Radiative energy loss reduction in a plasma due to damping The strong quenching of jets and the suppression of hadron spectra at high transverse momenta are striking experimental observations made in high energy nuclear collisions. Both have been interpreted as signature for the formation of a deconfined plasma of QCD matter, in which partons suffer a medium-induced energy loss. In theoretical studies devoted to a parton's radiative energy loss, however, the damping of radiation within the plasma has so far widely been neglected. We investigate the radiative energy loss per unit distance of a relativistic colour charge traversing as probe an infinite absorptive plasma. The Landau-Pomeranchuk-Migdal effect is incorporated as well as modifications due to the polarization of and damping mechanisms in the medium. The latter are phenomenologically described by a complex index of refraction, while the colour charge dynamics is considered in the Abelian approximation. We find a substantial reduction of the medium- induced mechanical work in addition to the well known Ter- Mikaelian effect from the polarization of matter. Moreover, the formation time of radiated quanta is also drastically reduced, both for small frequencies, where damping has a minor additional impact besides the polarization effect, and for larger frequencies. These effects are more pronounced for larger medium damping and/or larger initial energy of the charge. Therefore, we expect that our study will have a significant impact on the understanding of jet quenching phenomena in ultra- relativistic heavy-ion collisions at RHIC and even more at LHC. Speaker: Dr Marcus Bluhm (Laboratoire SUBATECH) • 151 Spectrum of initial fluctuations in the little bang We discuss an ab initio computation of the initial spectrum of fluctuations in the pre-equilibrium Glasma formed in heavy ion collisions [1]. Our result resums to all loop orders the leading unstable quantum fluctuations at early times. We showed explicitly previously for a scalar field theory [2] that averaging over the analogous spectrum of initial fluctuations leads to hydrodynamic behavior. The computation can now be carried out for QCD and we outline the algorithm for doing so. In addition to providing a mechanism for early thermalization, our result for the small fluctuation spectrum also enables one to compute a) key features of jet modification at early times and b) sphaleron transition rates in the Glasma. An understanding of the latter is crucial for the charge separation mechanism in the Chiral Magnetic Effect. We relate our weak coupling albeit non-perturbative results to strong coupling approaches to thermalization. References: [1] K. Dusling, F. Gelis and R. Venugopalan, manuscript in preparation. [2] K. Dusling, T. Epelbaum, F. Gelis and R. Venugopalan, Nucl. Phys. A850:69 (2011). Speaker: Dr Raju Venugopalan (Brookhaven National Laboratory) • 152 Cold nuclear matter physics at low-x from d+Au collisions at PHENIX RHIC experiments have observed that inclusive hadron yields in the forward rapidity (deuteron) direction for$\sqrt{s_{NN}} = 200$GeV d+Au collisions are suppressed relative to p+p collisions. The mechanism for the suppression has not been firmly established; theoretical descriptions include nuclear shadowing, initial-state parton energy loss, and gluon saturation. We present measurements by the PHENIX experiment at RHIC of di-hadron pair production in d+Au collisions where the particles in the pair are varied across a wide range of rapidity out to$|\eta| = 3.8$using a new forward electromagnetic calorimeter, the MPC. These di-hadron measurements probe down to parton momentum fractions x ~$10^{-3}$in the gold nucleus, where the interesting possibility of observing gluon saturation effects at RHIC is the greatest. Our measurements show that the correlated yield of back-to-back pairs in d+Au collisions is suppressed by up to an order of magnitude relative to p+p collisions, and increases with greater nuclear path thickness and with decreasing parton x in the Au nucleus. Speaker: Dr Mickey Chiu (Brookhaven National Lab) • 153 Initial state fluctuations at RHIC and LHC: hadronic or partonic origin? This talk will discuss how triangular flow measurements in Pb+Pb collisions at the LHC can be used to constrain the origin of initial state fluctuations. We explore the energy dependence of elliptic and triangular flow within a (3+1)-dimensional hybrid framework starting from a non-equilibrium initial state with event-by-event fluctuations and including an ideal hydrodynamical expansion phase followed by hadronic Boltzmann transport. This approach has been shown to describe well the existing RHIC and LHC data on bulk observables such as particle yields, spectra and elliptic flow. The initial energy deposition can be modeled either in a partonic or a hadronic picture using, respectively, a parton cascade or the hadronic transport model UrQMD. We present a detailed comparison between the shape and fluctuations of the two initial conditions prior to the hydrodynamical evolution. Our analysis then compares the differences in final state observables such as triangular flow in order to identify sensitivities to the degrees of freedom driving the energy deposition. Speaker: Hannah Petersen (Duke University) • 154 Influence of tubular initial conditions on two-particle correlations Relativistic nuclear collisions data on two-particle correlations exhibit structures as function of relative azimuthal angle and rapidity. A unified description of these near-side and awayside structures is proposed for low to moderate transverse momentum. It is based on the combined effect of tubular initial conditions and hydrodynamical expansion. A 3+1 hydrodynamic approach with fluctuating tubular initial conditions, in addition to reproducing both the near and away-side structures [1], leads to a good qualitative agreement with various data: dependence on trigger/associated particle tranverse momentum and on centrality [2], difference in the away-side structure for in-plane/out-of plane triggers [3]. Some results on the relation between triangularity and triangular flow have also been obtained for this approach [4]. Since 3+1 hydrodynamics is a complicated scenario, we have also studied the effect of single tubes in 2+1 hydrodynamics. Contrary to expectations, the hydrodynamic solution shows that the high energy density tubes (leftover from the initial particle interactions) give rise to particle emission in two directions and this is what leads to the various structures [2], including the effect of in-plane/out-of plane triggers [3]. This description is sensitive to some of the initial tube parameters and may provide a probe of the strong interaction. [1] J. Takahashi, B.M. Tavares, W.L.Qian, R. Andrade, F. Grassi, Y. Hama, T. Kodama, N.Xu, Phys. Rev. Lett. 103 (2009) 242301 (arXiv:0902.4870), [2] R.P.G. Andrade, F. Grassi, Y. Hama,W.-L. Qian, Nucl.Phys. A854 (2011) 81 (arXiv:1008.0139), [3] ] R.P.G. Andrade, F. Grassi, Y. Hama, W.-L. Qian, work in progress, [4] F.G. Gardim, F. Grassi, Y. Hama, M. Luzum, J.-Y. Ollitrault, work in progress. Speaker: Frederique Grassi (Instituto de Fisica-Universidade de Sao Paulo) • 155 AAMQS: a non-linear QCD description of new HERA data at small-x Recent developments in the computation of the NLO improvement for non-linear QCD evolution equations has allowed, for the first time, for the consistent description of experimental data using a first principle approach. In particular, the Balitsky-Kovchegov equation including running coupling effects (rcBK) has been shown to provide an excellent global description of inclusive DIS data. I will present a global analysis of available data on inclusive structure functions measured in electron-proton scattering at small values of Bjorken-x, including the latest data from the combined HERA analysis on reduced cross sections. The resulting parametrizations allow for the reliable computation of physical observables in a kinematical region (relevant for both p-p and A-A programmes at the LHC) where the standard DGLAP based techniques are expected to fail. Also, the inclusion of the heavy quark contribution has resulted in a good description of the experimental data for the charm component of the proton structure function. Further, I will discuss the kinematical domain where significant deviations from NLO-DGLAP should be expected and a strategy to interface this approach, reliant on k_t factorization, with the commonly used collinearly factorized parton distribution functions. Also preliminary extensions for nuclei will be discussed. Speaker: Dr Paloma Quiroga Arias (LPTHE , UPMC Univ. Paris 6) • 156 Particle multiplicities in high-energy hadronic collisions at RHIC/LHC from CGC with local rcBK evolution A color glass condensate (CGC) model for particle productions at collider energies is confronted with the data at RHIC and LHC. When applying the CGC picture to high-energy scatterings at LHC (or higher) energies, we need to include the effects of the running coupling and the transverse expansion of the colliding hadrons. These two are appropriately incorporated here. Main features of our model include 1) fluctuations of the transverse positions of the nucleons in the projectile, 2) the Gaussian shape for the transverse profile of a nucleon to account for the transverse expansion of the nucleon with increasing energy, and 3) the x-evolution of the unintegrated gluon distribution by the running-coupling Balitsky-Kovchegov (rcBK) equation which is applied locally in the impact parameter space. We study the influence of initial condition for rcBK equation on particle production in high energy hadronic collisions. Specifically, the initial conditions provided by i) the naive McLerran-Venugopalan (MV) model and ii) the running coupling MV model with adjustable parameters are examined. The use of running-coupling MV model as the initial condition is necessary for the consistency with the evolution equation which includes the effects of the running coupling. Speaker: Prof. Hirotsugu Fujii (University of Tokyo) • Poster Session 2 + Wine and Cheese Tente Imperiale, Salons Berlioz AB/Verdi AB (Imperial Palace) ### Tente Imperiale, Salons Berlioz AB/Verdi AB #### Imperial Palace • Friday, May 27 • Heavy flavor and Quarkonia in medium: I Théâtre National ### Théâtre National #### Centre Bonlieu France Convener: Dima Kharzeev (Brookhaven National Laboratory) • 157 Applying the AdS/CFT correspondence to non-abelian plasmas Speaker: David Mateos (ICREA & U. Barcelona) • 158 PHENIX heavy flavor Speaker: Cesar luiz daSilva (Los Alamos National Lab) • 159 Heavy-flavor production in PbPb collisions at the LHC measured with the ALICE detector The ALICE experiment studies nucleus–nucleus collisions at the LHC in order to investigate the properties of QCD matter at extreme energy densities. The measurement of open charm and open beauty production allows to investigate the mechanisms of heavy-quark propagation, energy loss and hadronization in the hot and dense medium formed in high-energy nucleus-nucleus collisions. In particular, in-medium energy loss is predicted to be different for massless partons (light quarks and gluons) and heavy quarks at moderate momentum. The ALICE apparatus allows us to measure open heavy-flavour particles in several decay channels and with a wide phase-space coverage. We present the first results on the nuclear modification factors for heavy flavour particle production in Pb–Pb collisions at psNN = 2.76 TeV. Using proton–proton and lead–lead collision samples at ps = 7 TeV and psNN = 2.76 TeV, respectively, recorded during 2010, nuclear modification factors RAA(pt) were measured for D mesons at central rapidity (via displaced decay vertex reconstruction), and for electrons and muons from heavy flavour decays, at central and forward rapidity, respectively. Speaker: Andrea Dainese (INFN Padova) • 160 Common discussion with 3 speakers Speaker: Dima Kharzeev (Brookhaven National Laboratory) • 10:00 AM Coffee break Théâtre National ### Théâtre National #### Centre Bonlieu • Heavy flavor and Quarkonia in medium: II Théâtre National ### Théâtre National #### Centre Bonlieu France Convener: Dima Kharzeev (Unknown) • 161 Quarkonia measurements by the CMS experiment in pp and PbPb collisions CMS is fully equipped to measure hard probes in the di-muon decay channel in the high multiplicity environment of nucleus-nucleus collisions. Such probes are especially relevant for studying the quark gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. Quarkonia and bottomonia are sensitive to the evolution of the medium. In particular, the$J\psi$production in heavy ion collisions has been studied at different energies and with different collision systems without yet giving a global picture that is fully understood. Measuring the charmonium production at the LHC energies in PbPb collisions will help constraining predictions, in particular those expecting high recombination of prompt J/Psi or suppression in hot medium. We will review CMS J/Psi measurements in pp collisions at √sNN=7~TeV, which allow precision studies of quarkonia production and serve as a reference for the observation of hot nuclear effects. CMS is able to distinguish non-prompt J/psi from prompt J/psi in PbPb collisions, and will present the prompt J/psi production cross-section in PbPb inclusively and as a function of transverse momentum, rapidity and number of nucleons participating in the collision. Finally, we compare the B fraction measured in PbPb collisions with that measured in pp at various energies. The LHC centre-of-mass energy allows copious Y production in PbPb collisions. Detailed measurements of bottomonium will help characterize the dense matter produced in heavy-ion collisions beyond what was accessible at RHIC (mostly) with charmonia. The full spectroscopy of quarkonium states has been suggested as a possible thermometer for the QGP. With its excellent dimuon mass resolution, CMS has measured the three Y states in pp collisions. With the 2010 PbPb data sample, CMS has observed the Y(1S) as well as excited states. The$\Upsilon(1S)$cross-section is presented as a function of transverse momentum, rapidity and centrality, and excited state. Suppression of the excited state in PbPb will be discussed. Speaker: Catherine Silvestre (Los Alamos National Laboratory (LANL)-Laboratoire de Physique Subatomique et Cosmologie (LPSC, Grenoble)) • 162 Quarkonium measurements at the LHC with the ALICE detector ALICE detector has excellent performances to study quarkonium production in heavy-ion collisions at the LHC collider [1]. In this new energy regime, charmonium could reveal a privileged probe to study the properties of the high-density strongly interacting system formed in the early stages of high-energy heavy-ion collisions [2]. Bottomonium resonances will be abundantly produced, providing new constrains on theoretical models of quarkonium dissociation in QCD matter [1]. Additionally, ALICE will study quarkonium production in proton-proton collisions in which high particle multiplicity events could lead to the formation of high energy density matter as in heavy ions collisions [3]. In ALICE [4], quarkonium is measured down to pT = 0 via their mu+mu− decay channels in the ALICE muon spectrometer and via their e+e- in the ALICE central barrel. After a short description of the apparatus, the transverse momentum and rapidity distributions of inclusive J/Psi production cross section in proton-proton collisions at LHC energies will be presented. We will discuss the dependence on charged particle multiplicity of J/Psi yield in proton-proton collisions at sqrt(s) = 7 TeV. The number of reconstructed tracklets (η<1.6) in the silicon pixel detector is exploited to measure the charged particle density at mid- rapidity. Finally, the analysis of the inclusive J/Psi production in Pb-Pb collisions at a centre of mass energy of sqrt(sNN) = 2.76 TeV will be described. Preliminary results on the nuclear modification factor (RAA) and the central to peripheral nuclear modification factor (RCP) will be shown. [1] ALICE collaboration, PPR II, J. Phys. G32, 1295 (2006) [2] P. Braun-Munzinger and J. Stachel, Phys. Lett. B490, 196 (2000); R.L. Thews, M. Schroedter and J. Rafelski, Phys. Rev. C63, 054905 (2001); A. Andronic et al., Phys. Lett. B571, 36 (2003); L. Grandchamp, R. Rapp and G.E. Brown, Phys. Rev. Lett., 92, 212301 (2004). [3] K. Werner et al. arXiv:1010.0400v1 (2011); K. Werner et al., Phys. Rev. Lett. 106, 122004 (2011). [4] ALICE collaboration, J. Instrum. 3, S08002 (2008). Speaker: Gines Martinez-Garcia (Laboratoire de Physique Subatomique et des Technologies Associees) • 163 Common discussion with 2 speakers Speaker: Dmitri Kharzeev (Stony Brook U./BNL) • Flash talks Théâtre National ### Théâtre National #### Centre Bonlieu France Convener: Bikash Sinha (Saha Institute of Nuclear Physics) • 164 First measurement of Upsilon suppression Speaker: Rosi Reed (STAR) • 165 Measurement of the Nuclear Modification Factor of Electrons from Heavy Flavour Decays at Mid-Rapidity in Pb-Pb Collisions at 2.76 TeV with ALICE Speaker: Yvonne Chiara Pachmayer (Ruprecht-Karls-Universitaet Heidelberg) • 166 Probing nuclear parton densities and parton energy loss processes through photon + heavy-quark jet production in p-A and A-A collisions Speaker: Tzvetalina Stavreva (LPSC) • 167 Dimuon radiation at the CERN SPS within a hybrid evolution model Speaker: Elvira Santini (Frankfurt University) • 168 Local Parity Violation or Local Charge Conservation/Flow? Speaker: Hui Wang (Michigan state university) • 169 Production of (anti)nuclei in pp and PbPb collisions with ALICE at the LHC Speaker: Natasha Sharma (Department of Physics-Panjab University) • 170 Continuous Time Monte Carlo for QCD in the Strong Coupling Limit Speaker: Wolfgang Unger (ETH Zuerich) • 171 First B→J/ψ measurement in PbPb collisions at 2.76 TeV with the CMS detector Speaker: Mihee Jo (Korea University (KR)) • 12:45 PM Lunch break Restaurant la Voile, Brasserie du Parc/Rotonde du Parc (Imperial Palace) ### Restaurant la Voile, Brasserie du Parc/Rotonde du Parc #### Imperial Palace La Voile 200p + brasserie 500p • Global and collective dynamics Salons Ravel AB (Imperial Palace) ### Salons Ravel AB #### Imperial Palace Convener: Helmut Oeschler (Technische Universität Darmstadt) • 172 Measurement of elliptic flow in sqrt(s_NN)=2.76 TeV PbPb collisions with the ATLAS detector at the LHC. The measurement of the elliptic flow for charged particles in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV with the ATLAS detector will be presented in a wide range of pseudorapidity, transverse momentum and collision centrality. The elliptic flow is measured by correlating azimuthal angles of reconstructed particle tracks with the event plane angle obtained from forward calorimeters. A large pseudorapidity gap between the tracking system and forward calorimeters significantly reduces contributions from short-range non-flow effects. For the first time at this energy, elliptic flow is measured over 5 units of pseudorapidity, from -2.5 to 2.5, and over a broad range in transverse momentum, 0.5-20 GeV. The results will be discussed in the context of previous measurements and theoretical model predictions. Speaker: Adam Trzupek (Henryk Niewodniczanski Inst. Nucl. Physics, PAN) • 173 Event-by-event hydrodynamics and elliptic flow from fluctuating initial state We develop a framework for event-by-event ideal hydrodynamics to study the differential elliptic flow which is measured at different centralities in Au+Au collisions at Relativistic Heavy Ion Collider (RHIC). Fluctuating initial energy density profiles, which here are the event-by-event analogues of the eWN profiles, are created using a Monte Carlo Glauber model. Using the same event plane method for obtaining$v_2$as in the data analysis, we can reproduce both the measured centrality dependence and the$p_T$shape of charged-particle elliptic flow up to$p_T\sim2$~GeV. We also consider the relation of elliptic flow to the initial state eccentricity using different reference planes, and discuss the correlation between the physical event plane and the initial participant plane. Our results demonstrate that event-by-event hydrodynamics with initial state fluctuations must be accounted for before a meaningful lower limit for viscosity can be obtained from elliptic flow data. Speaker: Hannu Holopainen (University of Jyväskylä) • 174 Charge dependent azimuthal correlations in PbPb collisions at$\sqrt{s_{NN}} = 2.76$~TeV Separation of charges along the extreme magnetic field created in non-central relativistic heavy-ion collisions is predicted to be a signature of local parity violation in strong interactions. We report on results for charge dependent two particle azimuthal correlations with respect to the reaction plane for Pb-Pb collisions at$\sqrt{s_{NN}} = 2.76$~TeV recorded in 2010 with ALICE at the LHC. The results are compared with measurements at RHIC energies and against currently available model predictions for LHC. Systematic studies of possible background effects including comparison with conventional (parity-even) correlations simulated with Monte-Carlo event generators of heavy-ion collisions will be also presented. Speaker: Dr Panos Christakoglou (NIKHEF - Utrecht University) • 175 Search for local strong parity violation in STAR using multiple observables Parity-odd domains from QCD are predicted to cause charge separation of quarks across the reaction-plane created in non-central relativistic heavy ion collisions--The Chiral Magnetic Effect [1]. Here we present several measurements to search for charge separation across the reaction-plane at STAR. We use three different observables: a three point correlator, a multiplicity asymmetry correlator, as well as a reaction-plane dependent balance function. The correlations are studied differentially and are presented for several Au+Au collision energies: 200, 62.4, 39, 11.5, and 7.7 GeV. We will discuss the sensitivities of these latest measurements to possible parity odd signals and parity even backgrounds. Speaker: Dhevan Gangadharan (Department of Physics-Ohio State University) • 176 Midrapidity charged particle directed flow in PbPb collisions at sqrt{s_{NN}} = 2.76 TeV measured with ALICE at the LHC Azimuthal anisotropic flow is a key observable indicating collectivity among particles produced in non-central heavy ion collisions. Directed flow is characterized by the first harmonic coefficient in the Fourier decomposition of the particle azimuthal distribution with respect to the collision reaction plane. It develops at a very early stage of the collision and thus is sensitive to the properties and the equation of state of the hot and dense matter produced in ion-ion collisions. We report on results for midrapidity (|eta|<0.8) charged particle directed flow measured in lead-lead collisions at 2.76 TeV collision energy recorded with the ALICE detector at the LHC. The orientation of the collision reaction plane is reconstructed with the help of the spectator neutrons detected by the pair of ALICE Zero Degree Calorimeter detectors. Directed flow results obtained with different measurement techniques are presented as a function of collision centrality, charged particle transverse momentum, and pseudo-rapidity. Speaker: Dr Ilya Selyuzhenkov (EMMI/GSI) • 177 Viscous hydrodynamic evolution with non-boost invariant flow for the color glass condensate The heavy ion program at LHC opened up a new era in the physics of the quark-gluon plasma (QGP) at higher energies. One of the most unique properties of the hot matter is the near-perfect fluidity, which was first discovered in Au-Au collisions at RHIC [1]. Relativistic hydrodynamic analyses on the momentum anisotropy of transverse collective flow revealed that small viscosity in the QGP is essential when the initial conditions are constructed from the color glass condensate (CGC), the description of saturated gluons in the nuclei before collisions. On the other hand, the dynamics of the longitudinal flow has scarcely been discussed so far due to the numerical difficulties of the non-boost invariant viscous hydrodynamic analyses in relativistic coordinates. Since the CGC itself is considered to be successful in reproducing the observed rapidity distributions and multiplicities at RHIC, it would be indispensable to investigate the longitudinal hydrodynamic evolution for the CGC. We develop a viscous hydrodynamic model with both shear and bulk viscosity and solve the full second-order constitutive equations [2] in the longitudinal direction with the relativistic coordinates using a novel numerical approach. The estimations are performed with the CGC-type initial distributions for both RHIC and LHC settings. The results exhibit visible and non-trivial deformations of the CGC rapidity distributions during the hydrodynamic stage due to the interplay between two factors: (i) Entropy production from non-equilibrium processes and (ii) entropy flux to the forward rapidity caused by non-boost invariance [3]. We find difference in the hydrodynamic effects at RHIC and LHC, which implies that readjustment of the CGC parameters might be necessary. This would be one of the possible explanations for the fact that the CGC predictions tend to underestimate the multiplicity at mid-rapidity observed in the Pb-Pb collisions at LHC experiments [4]. The results indicate that non-boost invariant hydrodynamic evolution together with viscosity is indispensable for understanding the physics of relativistic heavy ion collisions as a whole. We also obtain several important numerical insights towards a full (3+1)-dimensional viscous hydrodynamic model for the more quantitative analyses. References: [1] http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=05-38 [2] A. Monnai and T. Hirano, Nucl. Phys A 847, 283 (2010) [3] A. Monnai and T. Hirano, arXiv:1102.5053 [nucl-th] [4] K. Aamodt et al. [The ALICE Collaboration], Phys. Rev. Lett. 105, 252301 (2010) Speaker: Akihiko Monnai (The University of Tokyo) • Heavy Flavors Rotonde de l'Europe (Imperial Palace) ### Rotonde de l'Europe #### Imperial Palace Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Convener: Itzhak Tserruya (Department of Particle Physics-Weizmann Institute of Science) • 178 D meson nuclear modification factors in PbPb collisions at$\sqrt{s_{NN}}=2.76~{\rm TeV}$, measured with the ALICE detector The comparison of heavy flavour production in proton-proton and heavy-ion collisions allows to probe the properties of the high-density QCD medium formed in the latter and to study the mechanism of in-medium partonic energy loss. The ALICE experiment has measured the D meson production in pp and Pb--Pb collisions at the LHC at$\sqrt{s}=7$and$2.76~{\rm TeV}$and$\sqrt{s_{NN}} = 2.76~{\rm TeV}$respectively, via the exclusive reconstruction of hadronic decay channels. The D meson decay vertices, displaced by few hundred microns from the main interaction point, are selected by exploiting the high-resolution tracking performance and the hadron identification capabilities of the ALICE detectors. The analyses of the${\rm D^{0} \rightarrow K^{-}\pi^{+}}$and${\rm D^{+} \rightarrow K^{-}\pi^{+}\pi^{+}}$channels will be described and the preliminary results for the${\rm D^{0}}$and${\rm D^{+}}$nuclear modification factor will be presented. Speaker: Dr Andrea Rossi (Sezione di Padova (INFN)-Universita e INFN) • 179 Massive QCD antenna radiation in medium Medium modifications of jets have previously been thoroughly studied by calculating the gluon radiation spectrum off a highly energetic quark traversing a hot and dense QCD medium. But the study of the interference effects, the building block of the QCD jet calculation in vacuum, between different radiators has been missing for quite a long time. In this work we calculate, in the eikonal approximation, the gluon radiation spectrum off a quark-antiquark antenna passing through a deconfined QCD plasma with the masses of the quark and antiquark turned on. The massive quark-antiquark antenna involves both the dead cone effect and the Landau-Pomeranchuk-Migdal (LPM) effect, and takes into account the correlation between both of the emitters leading to an additional strong suppression of gluon radiation at angles smaller than the opening angle of the quark-antiquark pair. Furthermore, the quark-antiquark antenna spectrum is infrared divergent. We calculate the medium-induced energy loss of heavy quarks (charm and bottom) and compare it to well-known results (BDMPS/GLV). The implications on jet quenching observables in heavy ion collisions are also discussed. Speaker: Mr Hao Ma (Universidad de Santiago de Compostela) • 180 Recent PHENIX results on open heavy flavor Throughout the history of the RHIC physics program, questions concerning the dynamics of heavy quarks have generated much experimental and theoretical investigation. A major focus of the PHENIX experiment is the measurement of these quarks through their semi-leptonic decay channels at mid and forward rapidity. Heavy quark measurements in p+p collisions give information on the production of heavy flavor, without complications from medium effects. New measurements in d+Au indicate significant and surprising cold nuclear matter effects on these quarks at midrapidity, and provide a new baseline for interpretation of the observed suppression in Au+Au collisions. To complement the measured heavy quark spectra, correlations between heavy quark decay products give information on jet modification in nuclear collisions, while correlations between heavy quarks and hadrons produced in the same event can shed light on interactions with the medium. When considered all together, these measurements present a detailed study of nuclear matter across a wide range of system size and temperature. This talk will present new PHENIX measurements of non-photonic electron spectra and their centrality dependence in d+Au, and discuss their implications on the current understanding of parton energy loss in the nuclear medium. Speaker: J. Matthew Durham (Stony Brook University) • 181 Open charm hadron measurement in pp and Au+Au collisions at$\sqrt{s}$= 200 GeV in STAR Heavy quark production in elementary particle collisions are expected to be calculable in pQCD. In relativistic heavy ion collisions, heavy quarks are believed to be an ideal probe to study the properties of the created QCD medium. Early RHIC measurements were carried out mostly via semi-leptonic decay electrons. There are limitations in the electron approach: the charm hadron and electron kinematics are only weakly correlated due to the decay, and measured electrons have mixed contributions from various charm/bottom hadrons. Thus direct measurement of charm hadrons via hadronic decays is crucial to better understand charm-medium interactions at RHIC. In this talk, we will present the STAR preliminary results of D0 and D* in year 2009 p+p and D0 in year 2010 Au+Au collisions via hadronic decays covering$p_T$from 0.4 to 6 GeV/c in mid-rapidity |y|<1 at$\sqrt{s_{NN}}$= 200 GeV. Newly completed full barrel Time-Of-Flight detector was used in the analysis to improve the daughter hadron identification. The charm production$p_T$cross section in p+p collisions will be compared with pQCD calculations. The nuclear modification factors as a function of the collision centrality will be presented to discuss the number of binary collisions scaling of charm total cross-section. The behavior of D-meson freeze-out properties in Au+Au collisions will be compared with those of light and multi-strange hadrons. Preliminary results of the D0 decay vertex reconstruction in Au+Au collisions at$\sqrt{s_{NN}}$= 200 GeV from RHIC year 2007 using the silicon detectors of the STAR experiment will also be presented. Speaker: Dr Yifei Zhang (Lawrence Berkeley National Lab) • 182 Charmonium and open-charm production in p-A collisions at the SPS p-A collisions provide an essential reference for the study of J/psi suppression in heavy-ion data since they allow to evaluate cold nuclear matter effects. These include initial state effects like shadowing and parton energy loss and final state effects like J/psi breakup in the collisions with cold nuclear matter. To evaluate these, NA60 has measured J/psi production in p-A collisions at SPS energies with seven nuclear targets. In this analysis the J/psi cross section has been compared with open-charm production that is detected in the NA60 experiment through the simultaneous semi-muonic decay of D meson pairs. The comparison of the production of closed-charm with its natural reference allows to have some insight on how the interplay of the different processes gives rise to the observed (effective) J/psi suppression. Speaker: Dr Pietro Cortese (Univ. del Piemonte Orientale, Dip.Scienze eTecnologie) • 183 Heavy-flavor dynamics in nucleus-nucleus collisions: from RHIC to LHC The understanding of the heavy-quark dynamics in nucleus-nucleus collisions, so far possible at RHIC only through the inclusive measurement of electron spectra from c and b decays, is becoming now accessible at LHC also through the exclusive reconstruction of open-charm hadrons, thus providing a richer physical information useful to discriminate among different theoretical models. A complete setup to study heavy-flavor observables in pp and AA collisions was recently developed by us: in the latter case the presence of a hot fireball leads to a modification of the final p_T-spectra. More specifically, the propagation of c and b quarks in the plasma (whose evolution is supposed to be described by relativistic hydrodynamics) is followed by solving the relativistic Langevin equation within a picture of multiple uncorrelated random collisions. The relevant heavy-quark transport coefficients are given a microscopic evaluation within the Hard Thermal Loop approximation, supplemented by a kinetic pQCD calculation for hard collisions. The results obtained with this approach turned out to be in reasonable agreement with the experimental data obtained at RHIC, in particular for the R_AA of non-photonic electrons. Here we extend the above study to the LHC case, at the current center-of-mass energy of 2.76 TeV. The first data on primary charged particle density obtained by the ALICE collaboration (dN_ch/deta~1600 in central PbPb collisions) allow to provide an estimate of the initial conditions of the hydrodynamical evolution of the background medium. First results for the spectra, the R_AA and v_2 of open-charm hadrons and non-photonic single-electrons will be presented. Speaker: Dr Marco Monteno (INFN Torino) • Jets Salon Verdi AB (Imperial Palace) ### Salon Verdi AB #### Imperial Palace Convener: Nestor Armesto Perez (Universidade de Santiago de Compostela) • 184 Jet reconstruction with particle flow in heavy-ion collisions with CMS In the particle-flow approach one attempts to combine information from all available sub-detector systems to reconstruct all stable particles. Such an event reconstruction has been shown to improve the resolution of jets and missing transverse energy in pp collisions compared to purely calorimetric measurements. This is achieved primarily by combining the precise momentum determination of charged hadrons in the silicon tracker with the associated energy depositions in the calorimeters. By resolving individual particles inside jets, particle flow reduces the sensitivity of the jet energy scale to the jet fragmentation pattern, which is one of the largest sources of systematic uncertainty in jet reconstruction. Particle flow is thus an attractive tool for the study of potential modifications to jet fragmentation in heavy-ion collisions. The particle flow algorithm has been adapted to the heavy-ion environment. The performance of jet reconstruction from particle flow objects in PbPb collisions using the anti-kT jet reconstruction algorithm will be presented. Speaker: Matthew Nguyen (CERN) • 185 Jet quenching and elliptic flow in heavy ion collisions at RHIC and LHC within a pQCD-based partonic transport model We present fully dynamic simulations of heavy ion collisions at RHIC and at LHC energies within the perturbative QCD-based partonic transport model BAMPS (Boltzmann Approach to Multi-Parton Scatterings). We focus on the simultaneous investigation of high-pT observables, such as jet quenching, and bulk observables, such as the elliptic flow. The model features inelastic 2 <-> 3 processes based on the Gunion-Bertsch matrix element and has recently been extended to include light quark degrees of freedom. This allows for direct comparison to hadronic data on the nuclear modification factor via a fragmentation scheme for high-pT partons and also allows for the discussion of elliptic flow results in terms of a quark recombination picture. We present results on the nuclear modification factor of neutral pions at different centralities for Au+Au collisions at RHIC energies and compare to experimental data. First results on the nuclear modification of charged hadrons in central Pb+Pb collisions at the LHC are also presented and compared to recent ALICE data. Furthermore the differential elliptic flow of gluons and quarks as well as the centrality dependence of the integrated elliptic flow is studied within the same framework for Au+Au at RHIC and Pb+Pb at LHC. Speaker: Oliver Fochler (Institut für Theoretische Physik, Goethe-Universität Frankfurt) • 186 Higher harmonic jet tomography as a probe of fluctuating initial condition geometries in A+A While 2nd Fourier harmonics of jet quenching have been thoroughly explored in the literature and shown to be sensitive to (1) the underlying jet path length dependence of energy loss and (2) the differences between the mean eccentricity predicted by Glauber and CGC/KLN models of initial conditions, the sensitivity of higher harmonics, v_n(p_T, b), to differences between the fluctuation spectrum of geometries has remained relatively unexplored. We demonstrate that higher azimuthal jet harmonics (n>2) of R_AA(p_T,phi) and I_AA(p_T,phi) are remarkably insensitive to the differences of geometrical density fluctuations comparing between Glauber and CGC/KLN models of the initial conditions. Therefore, the differential elliptic v_2(p_T) vs. v_2^(I_AA)(p_T) moment correlation between the 2nd moment of monojet R_AA and dijet I_AA nuclear modifications factors remains the most sensitive probe to differentiate between Glauber and CGC/KLN initial state sQGP geometries. Speaker: Barbara Betz (Columbia University) • 187 Leading hadron PID effects in di-hadron angular correlations in STAR Hard scatterings of partons provide a valuable colored probe of the strongly-coupled medium created in ultra-relativistic heavy ion collisions. These hard scatterings can be studied by means of angular correlations of charged hadrons with respect to a high transverse momentum trigger particle. Several recent two-particle correlation studies indicate that A+A collision dynamics evolve significantly with collision centrality. They specifically reveal the presence of unexpected strong away-side deformation and the development of a long-range "ridge" in correlation measured as a function of$\Delta\eta$vs$\Delta\phi$. The detailed physics mechanisms responsible for these features however remain under active investigation. We will present preliminary results of a new di-hadron correlation analysis, measured as a function of$\Delta \phi$vs$\Delta \eta$, for identified high-pT triggers from the high-statistics 200 GeV Au+Au data sample collected by the STAR experiment at RHIC during Run-10. The relativistic rise of the ionization energy loss dependence of particles measured in the STAR TPC is used to obtain a statistical separation of charged pions, kaons, and protons. The$\Delta \phi$vs$\Delta \eta$correlations measured in this work extend earlier measurements of azimuthal correlations (in$\Delta \phi$only) with identified hadron triggers, which, admittedly with large uncertainties, reported no significant dependence on a leading hadron identity. The added$\Delta \eta$dimension and improved statistics reveal a rich set of new features: the near-side ($ |\Delta \phi|<1$) associated hadron distributions with respect to high-pT pion, kaon and proton triggers exhibit distinctly different features for both "ridge" (large$\Delta \eta$and small$\Delta \phi$) and "jet-like" ($ |\Delta \phi|<0.7$excluding the ridge) particles. We will discuss the implications of these results in the context of the existing models and possible connection of the leading hadron ID with the color-charge and/or flavor of a hard-scattered parton. Speaker: Kolja Kauder (University of Illinois at Chicago) • 188 Anomalous baryon production and its interplay with jet energy loss at RHIC and LHC energies The study of the nuclear suppression factor of charged hadrons and neutral pions in AuAu collisions at RHIC energies indicated the possible appearance of an anomaly at higher pT-s: although protons are expected to be produced from gluons, but jet energy loss is less effective for them comparing to pion suppression. Fragmentation function and jet energy loss based explanation can not reproduce this phenomena, which opens a discussion on anomalous baryon production at high-pt. We investigated the appearance of non-perturbative hadron production channels connected to the formation of strong non-abelian fields, and their strength at RHIC and LHC energies. We performed calculations with time dependent strong fields and studied the quark-pair and diquark-pair production at high-pT to produce leading quarks and diquarks to be hadronized. The numerical results are presented and discussed. Speaker: Peter Levai (KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary) • 189 Jets, mach cone, hot spots, ridges, harmonic flow, dihadron and$\gamma$-hadron correlations in high-energy heavy-ion collisions Within the AMPT Monte Carlo model, fluctuations in the initial transverse parton density are shown to lead to harmonic flows. The net back-to-back dihadron azimuthal correlation after subtraction of contributions from harmonic flows still has a double peak that is independent of the initial geometric triangularity and unique to the jet-induced Mach cone and expanding hot spots distorted by radial flow. The longitudinal structure of hot spots also leads to a near-side ridge in dihadron correlation with a large rapidity gap. By successively randomizing the azimuthal angle of the transverse momenta and positions of initial partons, one can isolate the effects of jet-induced medium excitation and expanding hot spots on the dihadron azimuthal correlation. The double peaks in the net dihadron and$\gamma$-hadron correlation are quantitatively different since the later is caused only by jet-induced Mach cone. Reference: [1] Guo-Liang Ma and Xin-Nian Wang, arXiv:1011.5249 Speaker: Dr Guo-Liang Ma (Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800, China) • Theory developments Salon Berlioz AB (Imperial Palace) ### Salon Berlioz AB #### Imperial Palace Salle de l'Europe, Imperial Palace Convener: Dr Jean-Yves Ollitrault (IPhT Saclay) • 190 Some new results on high-energy "jet stopping" in AdS/CFT A very basic theoretical question is: How far does a high-energy excitation travel in a quark-gluon plasma, and how does that distance scale with energy? In weak coupling, the stopping distance scales with energy as E^(1/2), up to logarithms. In strongly-coupled plasmas with gravity duals, theorists have found that the maximum stopping distance scales instead like E^(1/3). In the latter case, we show that there can be an important distinction between typical and maximum stopping distances. For the strongly-coupled excitations we study, we find that the typical stopping distance scales as E^(1/4). Speaker: Peter Arnold (University of Virginia) • 191 Non-conformal holography of light and heavy quark jet quenching at RHIC and LHC We investigate the connection between the conformal anomaly in the confinement transition region and quenching of heavy and light quarks in heavy ion collisions at RHIC and LHC by using a new non-conformal holographic model with a dilaton field. Holographic thermodynamic properties of the sQGP are constrained by lattice QCD calculations. The string drag force model of jets is generalized to include both trailing and falling string scenarios. We compare the differential nuclear modification of light and heavy quark jets predicted by this model emphasizing the novel quark mass and energy dependence through the confinement transition region. Speaker: Andrej Ficnar (Columbia University, New York, USA) • 192 Determination of relaxation times at weak and strong coupling Using linear response theory, we derive [1] conditions for the retarded Green's function so that the linearized equation of motion of a dissipative current is reduced to a relaxation-type equation of the Israel-Stewart type [2]. We prove that this reduction can be done, if the singularity of the retarded Green's function closest to the origin is a simple pole on the imaginary axis. The relaxation time coefficient is then given by the location of this pole in the complex plane. This implies that previous attempts to derive the relaxation time from the generic long-wavelength, low-frequency (i.e., fluid-dynamical) limit of the retarded Green's function, via an expansion in terms of gradients of the fluid-dynamical variables, in general fail to give the correct result. For a dilute gas, this prescription gives a value for the shear relaxation time that, under certain simplifying assumptions, coincides with the one derived by matching relativistic fluid dynamics to kinetic theory [3]. This shows that transient fluid dynamics is determined by the slowest microscopic and not by the fastest fluid-dynamical time scale. This has important implications for the description of the collective motion of matter formed in ultrarelativistic heavy-ion collisions, where microscopic time scales and the lifetime of the system itself can be of the same order. We also prove that the long-wavelength dynamics of the shear stress tensor in a strongly coupled N=4 SYM plasma is not described by relaxation-type equations as in Israel-Stewart theory [2]. [1] G. S. Denicol, J. Noronha, H. Niemi, and D. H. Rischke, accepted for publication in Phys. Rev. D; G. S. Denicol, H. Niemi, J. Noronha, D. H. Rischke, [arXiv:1103.2476 [hep-th]]. [2] W. Israel and J. M. Stewart, Phys. Lett. 58 A, 213 (1976); Ann. Phys. (N.Y.) 118, 341 (1979). [3] G. S. Denicol, T. Koide, and D. H. Rischke, Phys. Rev. Lett. 105, 162501 (2010). Speaker: Prof. Dirk Rischke (Institut fur Theoretische Physik, Goethe University, and Frankfurt Institute for Advanced Studies (FIAS), 60438 Frankfurt am Main, Germany) • 193 Fluctuation, dissipation, and thermalization in non-equilibrium${\rm AdS}_5$black hole geometries We give a simple recipe for computing dissipation and fluctuations (commutator and anti-commutator correlation functions) for non-equilibrium black hole geometries. The recipe formulates Hawking radiation as an initial value problem, and is suitable for numerical work. We show how to package the fluctuation and dissipation near the event horizon into correlators on the stretched horizon. These horizon correlators determine the bulk and boundary field theory correlation functions. In addition, the horizon correlators are the components of a horizon effective action which provides a quantum generalization of the membrane paradigm. In equilibrium, the analysis reproduces previous results on the Brownian motion of a heavy quark. Out of equilibrium, Wigner transforms of commutator and anti-commutator correlation functions obey a fluctuation-dissipation relation at high frequency. Speaker: Derek Teaney (Stony Brook University) • 194 Electrical conductivity and thermal dilepton rate from quenched lattice QCD. We report on a continuum extrapolation of the vector current correlation function for light valence quarks in the deconfined phase of quenched QCD. This is achieved by performing a systematic analysis of the influence of cut-off effects on light quark meson correlators at T=1.5 Tc using clover improved Wilson fermions [1]. In addition new results at 1.2 and 3.0 Tc will be presented. The first two, non-vanishing thermal moments of the vector meson spectral function are determined and compared with those for free, massless quarks. We discuss resulting constraints on the electrical conductivity and the thermal dilepton rate in a quark gluon plasma. [1] H.-T. Ding et al. Phys.Rev.D83(2011)034504 Speaker: Dr Olaf Kaczmarek (University of Bielefeld) • 195 Jet modification from RHIC to LHC We calculate the modification of hard jets in dense extended matter in the higher-twist formalism. The single gluon emission spectrum from a hard quark due to multiple scattering in a medium is evaluated as a power series in inverse powers of the virtuality of the hard jet. Retaining corrections up to next to leading power, we calculate the medium modified fragmentation function by resumming the effect of multiple gluon emissions in a virtuality ordered DGLAP like evolution equation. This new formalism is applied to the computation of the$R_{AA}$in high-energy heavy-ion collisions at RHIC and LHC. The medium is modeled using viscous 2+1D fluid dynamics which has been tuned to describe both the spectra and the$v_{2}$at a$p_T$< 2 GeV. The sole parameter of the calculation$\hat{q}$is set proportional to the entropy density and is found to be approximately$2$GeV$^{2}/fm$at a plasma temperature of$T=350$MeV. Using this we obtain a satisfactory description of the centrality and transverse momentum dependence of the$R_{AA}$at RHIC as well as its dependence on the azimuthal angle. With no change in parameters we obtain a natural description of the rising$R_{AA}$as measured by the ALICE collaboration at the LHC. Some new results from a Monte-Carlo routine based on this formalism will also be presented. Speaker: Dr Abhijit Majumder (The Ohio State University) • 5:00 PM Coffee break Foyer (Imperial Palace) ### Foyer #### Imperial Palace • Electromagnetic probes Salon Haendel AB (Imperial Palace) ### Salon Haendel AB #### Imperial Palace Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Convener: Tapan Nayak (Variable Energy Cyclotron Centre (VECC)) • 196 Measurement of inclusive isolated photons in PbPb collisions with CMS In studies of the dense medium produced in ultra-relativistic heavy ion collisions, photons are important hard probes, since they are not expected to be modified by the medium. The measurement of isolated prompt photon production in PbPb collisions provides a test of perturbative quantum chromodynamics (pQCD) and the information to constrain the nuclear parton distribution functions. CMS has shown excellent isolation capabilities in pp collisions at the LHC using the shower shape method. In heavy-ion collisions, two independent methods, shower shape and isolation, are used to separate isolated photons from non-prompt photons. This is the first application of these pp photon isolation techniques in heavy ion collisions. Shower shape templates are created with studies of the response in the electromagnetic calorimeter. The latter method, based on the tracker and the calorimeter, is found to have consistent results with the former method. We report the first measurement of the transverse momentum spectra of isolated photons in PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon nucleon pair with the CMS detector. The results are compared to NLO calculations at an energy of 2.76 TeV. The centrality dependence of the nuclear modification factor will be reported for isolated prompt photons with pT from 20 GeV/c to more than 80 GeV/c. Speaker: Yong Kim (Massachusetts Inst. of Technology (MIT) Heacy Ion group (CMS)) • 197 Low mass dimuon production in proton-nucleus collisions at$\sqrt{s} = 27.5$~GeV with the NA60 experiment The study of the production of low mass vector and pseudoscalar mesons in proton-nucleus collisions represents a natural baseline for the heavy-ion observations, allowing to provide a reference in an environment of cold nuclear matter. In-medium modifications of the vector meson spectral functions were actually predicted to occur also in cold nuclear matter, though the experimental evidence at the moment is controversial. Proton-nucleus collisions also give access to the study of strangeness production as a function of the size of the nucleus, providing a robust ground for strangeness enhancement in nuclear collisions. Besides that, the study of the nuclear dependence of particle properties in proton-nucleus collisions, as the transverse momentum spectra and the production cross sections, is an effective tool to understand the dynamics of soft hadron interactions. The NA60 experiment has collected an unprecedented statistics of 180000 low mass muon pairs in proton-nucleus data at$\sqrt{s} = 27.5$~GeV exposing to the beam six target materials: Be, Cu, In, W, Pb and~U. The very good statistical accuracy and dimuon mass resolution allowed us to perform a precision measurement of the$\rho$line shape related the$T$parameter of the Boltzmann factor, which was measured for the first time in p-A collisions. The$\rho-\omega$interference was also investigated and preliminary results are reported. No evidence of in-medium effects is found. In addition, the electromagnetic transition form factors of the$\eta$and$\omega$mesons were also measured, with a significant precision improvement with respect to the previous measurements. The$\omega$results, compared to the latest theoretical developments, still show the presence of an anomaly which is not described by theory. For the$\omega$and$\phi$mesons, thanks to the good acceptance coverage, the transverse momentum spectra were measured down to zero$\pt$. Finally, the nuclear dependence of the production cross sections was investigated in terms of the power law$\sigma_\mathrm{pA} \propto \mathrm{A}^\alpha$, and the$\alpha$parameter was studied as a function of$\pt$. Speaker: Dr Antonio Uras (INFN Cagliari, IPNL Lyon) • 198 Characterizing cold nuclear matter effects through dielectrons in d+Au collisions at √NN = 200 GeV at PHENIX Electron-positron pairs are effective probes for investigating the hot, dense matter created in RHIC collisions because they are carry no color charge and therefore, once created, do not interact strongly with the medium. As a result, they retain characteristics of the full time evolution and dynamics of the system. Among the many features, the low mass region (m<1 GeV/c2) consists primarily of pairs from Dalitz decays of light hadrons and direct decays of vector mesons that can be modified by the medium, while the intermediate (1 Speaker: Jason Kamin (State University of New York at Stony Brook) • 199 Exploring compressed nuclear matter with HADES In the energy domain of 1-2 GeV kinetic energy per nucleon, HADES has been performed systematic studies of electron-positron production in C+C, Ar+KCl, p+p, d+p and p+Nb collisions. Our results demonstrate that electron pair emission in small collision systems, such as C+C, can essentially be explained as a superposition of independent N+N collisions with a dominant contribution from the p-n channel. The comparison of the N+N reference spectrum with the di-electron invariant-mass distribution measured in Ar+KC collisions shows a pronounced excess radiation. The properties of the excess as a function of the transverse mass are quantified. Further medium effects have been investigated in p+Nb interactions at 3.5 GeV by a direct comparison to p+p reactions measured at the same energy. Differential dielectron production cross sections have been extracted and can be compared in detail in the pi^{0}, eta and the vector meson regions. The results will be discussed and compared to the ones obtained in photo-induced reactions. Intriguing results were also obtained from the reconstruction of hadrons with open and hidden strangeness in Ar+KCl collisions. While the measured abundance of all reconstructed particles are well described assuming thermalization, the also reconstructed double-strange baryon Xi^{-} appears about ten times more abundant than expected. Also, the phi/omega ratio is much larger than the one measured in N-N collisions and does not require any OZI suppression. Further investigations of compressed nuclear matter by means of di-electrons as penetrating probes and strangeness production will be followed up over the forthcoming years with an upgraded HADES detector in Au+Au and Ag+Ag collisions. Speaker: Andrej Kugler (Nuclear Physics Institute) • 200 Direct photons at low transverse momentum -- a QGP signal in pp collisions at LHC We predict that direct photon production in pp collisions at 7~TeV will get at least 10 times enhanced compared to the next to leading order pQCD predictions, at low transverse momentum ($\pt\lesssim$10~GeV/c), due to the thermal photon emissions from a quark gluon plasma (QGP) formed in high multiplicity events. Thus the enhancement of direct photon production at low$\pt$can be a QGP signal in pp collisions. Speaker: Prof. Fuming Liu (Huazhong Normal University) • 201 Can transport peak explain the low-mass enhancement of dileptons at RHIC? We propose a novel relation between the low-mass enhancement of dielectrons observed at PHENIX and transport coefficients of QGP such as the charge diffusion constant D and the relaxation time \tau. The observed low-mass enhancement sets a lower-bound on the diffusion constant, D > 2/T, with T being temperature. To reach this lower bound, we start with the second-order relativistic dissipative hydrodynamics by Israel and Stewart. The linearized hydrodynamic equation in external electromagnetic field gives a spectral function which is parametrized by D and \tau. Combining the spectral function with the full 3D hydrodynamic evolution, theoretical dielectron spectra and the experimental data are compared. Detailed analysis shows that the low-mass dilepton enhancement originates mainly from the high-temperature QGP phase where there is a large electric charge fluctuation as obtained from lattice QCD simulations. Speaker: Dr Yukinao Akamatsu (Nagoya University) • Energy scan Salon Berlioz AB (Imperial Palace) ### Salon Berlioz AB #### Imperial Palace Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Convener: Gunther Roland (MIT) • 202 Identified hadron production from the RHIC beam energy scan program in the STAR experiment A current focus at RHIC is the Beam Energy Scan (BES) program to study the QCD phase diagram --- temperature ($T$) vs. baryon chemical potential ($\mu_B$). The BES program aims to verify some predictions from QCD: that a cross-over occurs at$\mu_B$= 0, and that there exists a first-order phase transition at large$\mu_B$and a critical point at an intermediate$\mu_B$. The spectra and ratios of produced particles can be used to extract$T$and$\mu_B$in different energies and system sizes. The Solenoidal Tracker At RHIC (STAR) experiment has collected data for Au+Au collisions at$\sqrt{s_{NN}}=$7.7 GeV, 11.5 GeV, and 39 GeV in year 2010. One of the advantages during the BES program was the enhanced particle identification with availability of full Time-Of-Flight detector. In addition, STAR collected Cu+Cu collisions at 22.4 GeV in year 2005. We present mid-rapidity spectra ($p_{T}$or$m_{T}-m_{0}$), rapidity density, average transverse mass, and particle ratios for identified hadrons from the STAR experiment. The centrality and transverse momentum dependence of the particle yields and ratios will be compared to existing data at lower and higher beam energies and to various transport models like AMPT and UrQMD. Collision dynamics are studied systematically in the framework of chemical and kinetic freeze-out and their properties extracted from the particle ratios and spectra. Speaker: Dr lokesh kumar (Kent State University) • 203 Collision energy dependence of the flow and spectra results in Au+Au collisions at$\sqrt{s_{NN}}$= 7.7-200 GeV from PHENIX A central goal in experimental nuclear physics is to map out the QCD phase diagram, and to measure precisely the properties of the different phases. In order to achieve this goal, RHIC has embarked on an energy scan program involving gold nuclei at various energies. The data collected by the PHENIX experiment for this program consists of data sets obtained at$\sqrt{s_{NN}}$= 200, 62, 39 and 7.7 GeV. The analysis of these data, have yielded a wealth of new soft physics results which are used in concert to probe reaction dynamics and to constrain the transport coefficients of hot QCD matter. One particularly effective probe that is emphasized in this talk is the anisotropy of particle production, characterized by flow coefficients$v_{2}$and$v_{4}$. For Au+Au collisions at$\sqrt{s_{NN}}$= 200 GeV, measurements indicate a hydrodynamic flow of hot QCD matter at the partonic level with a small but finite value of the viscosity to entropy density ratio. However, at sufficiently low collision energy (thus lower energy density and temperature), we expect this picture to break down. Therefore measurement of the collision energy dependence of$v_{2}$and$v_{4}$could provide new insights to the current understanding of the nature of interactions in hot QCD matter. We present new energy scan measurements of flow coefficients for both unidentified and identified particles, as well as several other soft physics observables such as identified hadron spectra and HBT correlations. The implications of these results will also be discussed. Speaker: Xiaoyang Gong (Stony Brook University) • 204 QCD critical point and event-by-event fluctuations Observables measuring the magnitude and non-Gaussianity of event-by-event fluctuations can be used to discover the QCD critical point in heavy-ion collisions. I shall describe theoretical predictions for the non-Gaussian measures such as skewness, kurtosis and corresponding mixed moments as a function of the beam energy in the presence of the QCD critical point. I shall discuss implications for the RHIC Beam Energy Scan and what we can learn from recent data. Speaker: Prof. Misha Stephanov (UIC) • 205 Energy dependence of the freeze out eccentricity from azimuthal dependence of HBT at STAR Non-central heavy ion collisions at RHIC create an anisotropic participant zone of QCD matter under extreme conditions of energy and matter density. While this zone is initially out-of-plane-extended, pressure gradients cause the hot, dense medium to expand preferentially in plane. Over time, this expansion makes the shape more spherical, perhaps even becoming extended in the in-plane direction. The change in shape is determined by the expansion and freeze-out time scales which depend, in part, on the early pressure gradients. As a result, the freeze-out shape may provide a sensitive probe of the Equation of State of hot QCD matter. The recent RHIC Beam Energy Scan at$\sqrt{s_{NN}}$of 7.7, 11.5, and 39 GeV provides an opportunity to explore the energy dependence of the freeze out eccentricity. The new low energy data from STAR complements high statistics data sets at$\sqrt{s_{NN}}$of 62.4 and 200 GeV. The dependence of the HBT radius parameters on azimuthal angle relative to the reaction plane have been extracted. These dependences can be related to the freeze out eccentricity within the context of a blast wave model. We will present STAR's most recent results on azimuthally-dependent HBT across a wide range of energies. Speaker: Christopher Anson (The Ohio State University) • 206 Energy dependence of energy loss in Au+Au collisions at PHENIX The suppression of inclusive pion production by up to a factor of 5, which was first observed in Au + Au at √sNN= 130 GeV/c (e.g. [1]) and later in Au + Au at √sNN= 200 GeV/c [2, 3], is one of the most significant manifestations of the opaque QGP produced in heavy ion collisions. The absence of this suppression in d + Au collisions at the same energy indicates the final state nature of the suppression. It is natural to ask where the onset of such massive suppression is in terms of the energy density of the medium which is dictated by the collision energy, centrality and the mass of colliding nuclei. The PHENIX collaboration has studied collisions of lighter nuclei (Cu + Cu) at different beam energies in 2005 [4]. While a significant suppression is observed both at √sNN = 200 and 62.4 GeV, at √sNN = 22.4 GeV a moderate enhancement is found. In 2010 RHIC scanned lower energies, and PHENIX collected substantial data sets in Au + Au collisions at √sNN = 39 and 62 GeV. The goal was to identify better the conditions for the onset of the π0 suppression. This talk presents results from the systematic study of c.m. energy and the system size dependencies of π0 yield and the nuclear modification factor. References [1] K. Adcox et al., Phys.Rev.Lett. 88, 022301 (2002). [2] S. S. Adler et al., Phys.Rev.Lett. 96, 202301 (2006). [3] A. Adare et al., Phys.Rev.Lett. 101, 232301 (2008). [4] A. Adare et al., Phys.Rev.Lett. 101, 162301 (2008). Speaker: Norbert Novitzky (Department of Physics-University of Jyvaskyla) • 207 Net-baryon-, net-proton-, and net-charged particle kurtosis in heavy-ion collisions within a relativistic transport approach We explore the potential of net-baryon, net-proton and net-charge kurtosis measurements to investigate the properties of hot and dense matter created in relativistic heavy-ion collisions. Contrary to calculations in a grand canonical ensemble we explicitly take into account exact electric and baryon charge conservation on an event-by-event basis. This drastically limits the width of baryon fluctuations. A simple model to account for this is to assume Poisson distributions with a sharp cut-off at the tails. We present baseline predictions of the energy dependence of the net-baryon, net-proton and net-charge kurtosis for central ($b\leq 2.75$~fm) Pb+Pb/Au+Au collisions from$E_{lab}=2A$~GeV to$\sqrt{s_{NN}}=200$~GeV from the UrQMD model. While the net-charge kurtosis is compatible with values around zero, the net-baryon number decreases to large negative values with decreasing beam energy. The net-proton kurtosis becomes only slightly negative for low$\sqrt{s_{NN}}$. Speaker: Marlene Nahrgang (Goethe University Frankfurt and Frankfurt Institute for Advanced Studies (FIAS)) • Global and collective dynamics Salon Ravel AB (Imperial Palace) ### Salon Ravel AB #### Imperial Palace Convener: Johannes Wessels (Institut fuer Kernphysik - Westfaelische Wilhelms-Universitaet M) • 208 Elliptic and triangular flow in the event-by-event 3+1D viscous hydrodynamics I will present results for elliptic and triangular flow coefficients v2 and v3 in Au+Au collisions at sqrt(s) = 200A GeV using event-by-event 3+1D viscous hydrodynamic simulations. I will report on the effect of initial state fluctuations and finite viscosities on the flow coefficients v2 and v3 as functions of transverse momentum and pseudo-rapidity. I will argue that simultaneous measurements of v2 and v3 can determine the shear viscosity-entropy ratio more precisely. I will also touch upon recent calculations of v2 and v3 for the LHC heavy ion collisions. Speaker: Sangyong Jeon (McGill University) • 209 Elliptic flow at high transverse momentum in PbPb collisions at$\sqrt{s_{NN}} = 2.76$~TeV with the ALICE experiment As a consequence of the energy loss of highly energetic parton propagating through a dense medium, jet quenching is an important probe of QGP created in high energy heavy-ion collisions. Jet quenching leads to the suppression of particle production at high transverse momenta. An observable that can be used to better constrain the mechanism responsible for the parton energy loss is the elliptic azimuthal event anisotropy,$v_2$, which provides differential information on the particle yield and jet quenching relative to the reaction plane. We report on measurements of the elliptic event anisotropy for unidentified charged particles with$p_T$up to 20~GeV/c in Pb-Pb collisions at$\sqrt{s_{NN}} = 2.76$~TeV recorded by the ALICE experiment at the LHC. Additionally, we report on measurement of$v_2$for identified particles with$p_T<10$~GeV/c; pions and protons are identified using the ionization energy loss in the TPC. The results are compared to the measurements at lower energy reported by RHIC experiments but also to theoretical predictions. Speaker: Alexandru Florin Dobrin (Wayne State University) • 210 Turbulent fluctuations around Bjorken flow For large Reynolds number (which is inverse to viscosity), fluids are known to develop turbulence. Therefore, the phenomenological evidence for a small viscosity suggests that the hydrodynamical description of heavy ion collisions may have a turbulent regime. Assuming that averaged velocities are described by Bjorkens model, we investigate local fluctuations around it. These perturbations are governed by non-linear equations and we characterize classes of qualitatively different evolution in terms of Reynolds numbers. Perturbations at different rapidities are found to decouple quickly, and the local evolution becomes effectively two-dimensional. The resulting Navier-Stokes equation of non-relativistic form (obtained after suitable coordinate transformations) can be discussed within the theory of Kolmogorov and Kraichnan. In particular, unlike three-dimensional turbulent flow, two-dimensional viscous fluid dynamics can show the interesting phenomenon of inverse cascading of energy into large scale structures. We speculate on possible phenomenological implications of these findings. Speaker: Dr Stefan Floerchinger (CERN) • 211 Far-from-equilibrium anisotropic collective flow Novel analytical results for the anisotropic collective flow of massive particles with a small interaction cross-section are presented. In particular, we show that, even when particles rescatter at most once, a sizable elliptic flow$v_2$is generated, with mass ordering of the various particle species. Speakers: Dr Clément Gombeaud (University of Bielefeld), Prof. Nicolas Borghini (University of Bielefeld) • 212 Identified particles from viscous hydrodynamics Much of our understanding of the collision dynamics at RHIC and LHC relies on contrasting hydrodynamic or hydro+transport calculations with experimental data. For example, early evidence for rapid thermalization and quark-gluon plasma phase transition at RHIC came from particle spectra and the pion-proton splitting of differential elliptic flow. An inevitable component in these calculations is the conversion of the fluid to particles. For an ideal fluid the conversion is straightforward (the usual caveats of the Cooper-Frye treatment aside) because the phase space distributions are locally thermal for each species. For a viscous fluid, however, an infinite class of phase space corrections can reproduce the same hydrodynamic variables, even in a one-component system. Present viscous hydrodynamic calculations routinely assume that phase space corrections induced by shear stress are quadratic in momentum and that they have the same coefficient for all particle species ("democratic" Grad ansatz), independently of microscopic details. However, in a gas of hadrons, equilibration is driven by scattering rates - species that scatter rarely tend to be further away from local equilibrium than those that scatter often. We will present results from fully nonlinear covariant transport theory for the phase space corrections in an expanding multicomponent gas, and test the validity of Grad's quadratic ansatz and of the "democratic" assumption for sharing viscous effects between species. The findings will be compared to phase space corrections from linear response theory, which is applicable for small gradients and small deviations from local equilibrium. Finally, we will show how dynamical phase space corrections affect basic identified particle observables (spectra and elliptic flow) in the framework of viscous hydrodynamics. Speaker: Denes Molnar (Purdue University) • 213 Measurement of the electromagnetic dissociation cross-section of Pb nuclei at 2.76 A Tev with the ALICE ZDC Electromagnetic dissociation of heavy nuclei in ultra-peripheral interactions at high energies can be used to monitor the beam luminosity at colliders. Neutrons emitted by the excited nuclei close to beam rapidity are detected by the ALICE Zero Degree Calorimeters (ZDC) with full acceptance, providing a precise measurement of the event rate. During the 2010 Pb-Pb run, a dedicated data taking has been performed triggering on electromagnetic processes with the ZDC. These data, combined with the results from the Van der Meer scan, allow one to measure the dissociation cross-section of Pb nuclei at sqrt(s)=2.76 A TeV. Experimental results on the cross-section for electromagnetic dissociation processes of Pb nuclei at the LHC will be presented together with a comparison to the available predictions. Speaker: Dr Chiara Oppedisano (INFN, Sezione di Torino) • Jets Salon Verdi AB (Imperial Palace) ### Salon Verdi AB #### Imperial Palace Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Salle de l'Europe, Imperial Palace Convener: Barbara Jacak (Stony Brook University) • 214 Dijet fragmentation functions measured in PbPb collisions with CMS The energy loss of fast partons traversing the strongly interacting matter produced in high-energy nuclear collisions is one of the most interesting observables to probe the nature of the produced medium. Analyzing data from PbPb collisions at a center-of-mass energy of 2.76 TeV, recorded with the Compact Muon Solenoid (CMS) detector, parton energy loss is observed as a significant imbalance of dijet transverse momentum. To gain further understanding of the parton energy loss mechanism and how it manifests itself in the distribution of final state particles, parton fragmentation functions are studied for the leading and subleading jet in bins of centrality and dijet imbalance. Dijets are reconstructed using the anti-kT jet algorithm, with the particle flow method of event reconstruction. Particle flow, which is applied to heavy-ion collisions for the first time in this measurement, allows for improved jet reconstruction by combining track and calorimeter information at the particle level. The fragmentation functions for leading and subleading jets are compared to model calculations and measurements in pp collisions. The results confirm and complement earlier CMS results based on calorimeter jets and yield a detailed picture of parton propagation in the hot QCD medium. Speaker: Yetkin Yilmaz (Massachusetts Inst. of Technology (MIT)) • 215 Jet shower evolution in medium and di-jet asymmetry in PbPb collisions at the LHC We study the evolution of a partonic jet shower propagating through a hot quark-gluon plasma. A differential equation is derived the evolution of the radiated gluon distribution as the jet propagates through the medium. Combined with the in-medium evolution of the leading parton, we compute the depletion of the energy from the jet cone by dissipation through elastic collisions with medium constituents, by scattering of shower partons to larger angles, and by radiation outside the jet cone. Numerical results are presented for the nuclear modification of di-jet energy asymmetry in Pb+Pb collisions at the LHC. Speaker: Guang-You Qin (Duke University) • 216 Jet-Hadron Correlations in STAR In recent years, the study of dihadron correlations has been one of the primary methods used to investigate the propagation and modification of hard-scattered partons in the QGP. Due to recent advancements in jet-finding algorithms it is now possible to use reconstructed jets in these correlation studies. This increases the kinematic reach of such analyses and improves the signal-to-background ratio. We show results of a systematic study of jet-hadron correlations in 200 GeV central Au+Au collisions, which are indicative of a broadening and softening of jets which interact with the medium. Furthermore, jet-hadron correlations suggest that the suppression of the associated hadron yield at high-$p_{T}$is balanced by low-$p_{T}\$ enhancement.
Speaker: Alice Ohlson (Yale University)
• 217
Monte-Carlo simulation for elastic energy loss of high-energy partons in a hydrodynamical background
We examine the significance of elastic collisions as the suppression mechanism of high-energy partons in the strongly interacting medium formed in ultrarelativistic heavy ion collisions. For this purpose, we have developed a Monte Carlo simulation describing the interactions of perturbatively produced, non-eikonally propagating high-energy partons with the quarks and gluons from the expanding QCD medium. The partonic collision rates are computed in leading-order perturbative QCD, while three different hydrodynamical scenarios are used to model the QCD medium: (1+1)-dimensional hydro with initial conditions from the EKRT model for central heavy ion collisions, (2+1)-dimensional hydro with a smooth sWN profile obtained from the optical Glauber model for non-central collisions, and event-by-event hydro with an eBC profile from the Monte Carlo Glauber model to study the initial state fluctuation effects. We compare our results with the neutral pion suppression observed in sqrt(s_NN)=200 GeV Au+Au collisions at the BNL-RHIC. We find the incoherent nature of elastic energy loss incompatible with the measured data. Also the effect of the initial state fluctuations appears to be negligible.
Speaker: Mr Jussi Auvinen (University of Jyväskylä)
• 218
Can we see from jet quenching that quark-gluon plasma becomes more perturbative at LHC than at RHIC
We study the nuclear modification factor R_AA at RHIC and LHC energies. We account for the radiative and collisional energy losses. Both the contributions are calculated with running \alpha_s accounting for fluctuations of the jet path lengths. The effect of the thermal suppression of \alpha_s is investigated. Comparison of the theoretical results with the experimental data obtained at RHIC and in the ALICE experiment at LHC demonstrates that the experimental R_AA may be described in pQCD with the entropy extracted from the multiplicity data. However for LHC the thermal suppression of \alpha_s should be stronger. This fact demonstrates that at LHC the quark-gluon plasma becomes more perturbative.
Speaker: Bronislav Zakharov (Landau Institute)
• 219
Medium induced collinear radiation from soft collinear effective theory (SCET)
The propagation of hard partons through the strongly interacting matter created in high energy heavy-ion collisions involves widely separated scales. The methods of Effective Field Theories (EFT) can provide a factorized description at lowest nontrivial order, and a formalism where the correction to this factorization are calculable systematically order by order in the small ratios between the different scales. In this talk I will present our recent results on the calculation of the spectrum of the gluons emitted by the hard parton, where the radiated gluons are collinear with the incoming hard parton and with arbitrary energy (not necessarily much softer than the energy of the hard parton). I will also briefly discuss how to extend the analysis to include the emission of gluons collinear in arbitrary directions and gluons with all the components of their momentum scaling as the medium characteristic energy scale (soft gluons). In particular I will show how powerful concepts like collinear gauge invariance and reparameterization invariance simplify the derivation of the effective Lagrangian.
Speaker: Mr Francesco D'Eramo (MIT)
• 8:00 PM
Banquet Brasserie du Parc/Rotonde du Parc, Restaurant la Voile, Rotonde de l'Europe, Salle de l'Europe (Imperial Palace)

### Brasserie du Parc/Rotonde du Parc, Restaurant la Voile, Rotonde de l'Europe, Salle de l'Europe

#### Imperial Palace

• Saturday, May 28
• PRIZES and AWARDS Théâtre National

### Théâtre National

#### Centre Bonlieu

France
• New challenges Théâtre National

### Théâtre National

#### Centre Bonlieu

France
Convener: Johanna Stachel (Physikalisches Institut)
• 220
The low energy frontier of A-A
Speaker: Marcus Bleicher (Uni Frankfurt)
• 221
Physics opportunities of future p-A runs
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Physics opportunities of e-A colliders
Speaker: Anna Stasto (Penn State University)
• 223
The high energy frontier of A-A
Speaker: Federico Antinori (INFN Padova, Italy)
• Closing Théâtre National

### Théâtre National

#### Centre Bonlieu

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• 224
Presentation of QM12
Speaker: John Harris (Yale)
• 225
Closing